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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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gmatt1476 wrote:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission. Thus, any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.

The reasoning above exhibits a flaw similar to one in which of the following?

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.
D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.


CR78561.01


Law since 1978 - New books should not be copied without permission.
Conclusion - Any books copied without permission must have been old.

We are concluding that all books copied must have been old only because there is a law in place. We are assuming that everyone followed the law. This is our flaw.

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

The premise tells us how "member of the solar system" is defined. It must be a planet or a moon.
So we can conclude that anything that is not a planet or a moon cannot be called a member of the solar system.
This is fine.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.

Law - anyone who rides the city bus must buy a pass.
Demetrios has a pass.
Conclusion - He must be riding the city bus.

This is not correct. There is a flaw here but it is of assuming a necessary condition to be sufficient. A bus pass is necessary for riding the bus. But does having a bus pass mean that one does ride the bus? Not necessary. What if there are other things that need a bus pass too such as for identity?

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.

Law - a driver who turns right must signal.
Anyone who did not signal did not turn right.

We are making the same assumption here as we did in our original argument - everyone follows the law. If one did not signal, it means they did not turn right.

This is our answer.

D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

Not a flaw. This is logical. Law needs a passport to cross national boundary. So if one does not have a passport, he cannot "legally" cross a national boundary. Mind you, he can still cross a national boundary if he doesn't follow the law but LEGALLY he cannot. That is correct.
Hence not our answer.

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.

This is exactly same as our option (B).
State taxes are a must (necessary) for wage earners residing in the state. That means everyone who pays state taxes must be a resident of the state? Not true. What if Non residents also need to pay taxes? There is a flaw in this argument but not the same as our original argument. Here necessary condition is taken to be sufficient - that is the flaw.

Answer (C)
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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gmatt1476 wrote:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission. Thus, any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.

The reasoning above exhibits a flaw similar to one in which of the following?

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.

D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.


CR78561.01


Official Explanation

Argument Evaluation

The flaw in which one of the five arguments presented is most similar to the flaw in the given argument?

The conclusion of the given argument is adequately supported by its premises only if supplemented by a highly implausible assumption: Since the 1978 copyright law came into force, no book published since 1978 has been photocopied without the publisher's permission.

However, this would be unreasonable to assume: we have no reason to assume that the existence of a rule implies compliance with that rule.

A. This argument contains no flaw; its conclusion follows logically from its supporting information.

B. This argument is flawed because it is possible that Demetrios is not riding on a city bus but yet still owns a bus pass. However, this is not an argument regarding compliance or non-compliance with a rule.

C. Correct. This argument has the same structure as the given argument. For the argument to work, it must be supplemented with the following highly implausible assumption: No driver who fails to signal turns right. That assumption is implausible because the existence of a rule is not always followed by compliance with that rule.

D. The conclusion drawn here follows logically from the premise on which it is based. Therefore, the argument is not flawed.

E. This argument is flawed: it is possible that Blodwen pays state taxes yet is not a resident in the state. The condition “liable to pay state tax” applies to all residents of the state, but we do not know that this applies only to residents of the state. That is, the class of those “liable to pay state tax” may in fact be larger than the class of those “resident in the state.” In any case, the structure of this argument is significantly different from the given argument.

The correct answer is C.
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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[quote="gmatt1476"]Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission. Thus, any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.

The reasoning above exhibits a flaw similar to one in which of the following?

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.
D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.


such questions can be handled with ease .
Follow below steps
1)check if the logical flow has legal aspect or if the logical statement is dependent for result on a certain circumstance .
2)name the logic in form of X+ Y= z to get hang of the logic and so that you dont get lost in mid while eliminating .
3)choose the logic that logically looks like same circumstances as in question.

For example in this question
law changed (we see legal aspect involved , so any solution that has law involved will be best solution . If not then we will choose 2nd best option ) - Books less than 50 years old for copy (lest say B<50) - needs permission(lets say P) - thus any book copied without permission (No P)- is less than 50 years old (B>50) .(ASSUMING THAT NO ONE CAN BREAK LAW, so the book has to be at least 50 if they haven't taken permission. )

so in code words B<50 will have P .If no P then B is at least 50 years old .

Now lest have a look at options .

A. Any member(Y) of the solar system(S.S) must be either a planet or a moon(X), so if an asteroid (Y)is neither a planet nor a moon(NOT X), it must not be a member of the solar system (Not S.S) . we can conclude that Y of S.S =X If Y (Not X) Then Its No S.S . Yes This Looks like what teh statement tried to say But there is a little catch . This has no legal aspect involved . Plus our main stimulus said at least 50 years old which means If Y is not X then its at least not part of S.S .So A lacks these 2 aspects lets move on.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.
(X) (CB) must buy (BP) , (X) has (BP) It must Ride (CB)
option B is clearly not a contender because we need something that says If X needs Y ARE RELATED .If there is no Y then it is not B .

C. A driver who turns right must signal, so any driver who did not signal must not have turned right. (D who turn R must have S . If D has no S then the result is no R ) This is exactly what or stimulus is saying . It has used words like MUST . This whole statement like our stimulus follows a rule that must be followed by drivers who are abided by law. Moreover it contains info that anyone who does not have x IS NOT y. which resmbled our main coding if B is less than 50 then it must have P .If B has no P then B is more than B . Its as If saying MY TEDDY HAS RED DOT .IF THIS TEDDY HAS NOT RED DOT THEN ITS NOT MY TEDDY .

D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.
This is clear no becoz in first and second line its repeating the same logic . (I crossed NB so I have P . If you have no P then You can't cross B . Yes its obviously I cant cross B if I dont have P .This sentence is not rejecting the idea that any book that dosent have P is at least 50 or more .

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state. (same as D)
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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This argument is tricky, but you need to see that it confuses a Necessary condition for a sufficient one...(or maybe i've mixed my terms around).

Basically there are 2 valid forms of conditional statements:
1. Repeat Form:1. Repeat Form:
Logic of statement is restated.
Example: John received an A+ on the test, so he must have studied
Sufficient: A+ Necessary: Study

2. Contrapositive:
If necessary condition does not occur, then sufficient condition cannot occur
Scenario: John did not study, so he must not have received an A+


And 2 forms of invalid conditional statements:

1. Mistaken Reversal
MR reverses the necessary condition with the sufficient condition and although the statement might be true, it is not definitely true.
Scenario: John studied on the test, therefore he must have received an A+

2. Mistaken Negation
Just because the sufficient condition did not occur doesn't mean the necessary condition did not occur
Scenario: John did not receive an A+, so he must not have studied for the test


Mistaken Negation

C is correct because it replicates this logic:
It is necessary for someone turning right to signal
So any driver who did not signal (necessary) must not have turned right (sufficient)

I may have confused my terms...
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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gmatt1476 wrote:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission. Thus, any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.

The reasoning above exhibits a flaw similar to one in which of the following?

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.
D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.


CR78561.01



Statement A - books less than 50 years old
Statement B - not (photocopied without permission)
2nd half says:
photocopied without permission therefore must be at least 50 years old
Not B -> Not A
Logic : Contra-positive

A)
Statement A - Member of SS
Statement B - Planet or Moon
A -> B

2nd half says:
Not a planet or Moon therefore not part of SS
which implies Not B -> Not A

Valid : Contra-positive

B)
Statement A - Ride a city bus
Statement B - Must have a pass
A -> B

2nd half says:
Has a bus pass therefore riding a bus
which implies B -> A

Invalid : Revere Relationship or Mistaken Reversal
(But this flaw is not similar to one in the question)

C)
Statement A - Turns right
Statement B - Must signal

2nd half says:
Did not signal therefore did not turn right
which implies Not B -> Not A

Valid : Contra-positive

D)
Statement A - Legally cross border
Statement B - has passport
A -> B

2nd half says:
Not have a passport -> Not cross legally
Not B -> Not A

Valid : Contra-positive

E)
Statement A - residing in states
Statement B - must pay taxes
A -> B

2nd half says:
Pays taxes -> residing in states
B -> A

Invalid : Revere Relationship or Mistaken Reversal
(But this flaw is not similar to one in the question)

As evident statements A,C and D are having a similar pattern of logic. Among these statements A and D are pretty robust and can not be contradicted. D if contradicted would imply at "illegal" ways to cross border.
(This portion is explained pretty well by CJandAnish above :) )

Leaving us with the only possible option of C, which contains the same flaw as the question - that if a rule exists then everyone will follow the rule.

-------
Please feel free to provide your inputs to help me learn :)
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
Option A, C & D looked exactly identical to me.

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

Member of Solar System -> Planet or Moon
Neither Planet nor Moon -> Not a Member of Solar System (Contrapositive)

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.

Driver Turning Right -> Signal
No Signal -> Driver did not turn right (Contrapositive)

D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

Person Legally Crosses a boundary -> Passport
No Passport -> cannot legally cross a boundary (Contrapositive)

After reading all the posts I am still not convinced why should we reject A and D.
GMATNinja VeritasKarishma Could you please explain this question?

Is "the existence of a rule implies compliance with that rule" - the only factor differentiating correct and incorrect?
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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The contrapositive of IF A, THEN B is IF NOT B, THEN NOT A.
If an IF-THEN statement is true, its contrapositive is also true.
True IF-THEN statement:
If John is in Times Square, then John is in New York.
Contrapositive:
If John is not in New York, then John is not in Times Square.

gmatt1476 wrote:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission. Thus, any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.

The reasoning above exhibits a flaw similar to one in which of the following?

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.
B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.
C. A driver who turns right must signal, so any driver who did not signal must not have turned right.
D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.
E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.


CR78561.01


Premise of the passage:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission.
Rephrased as an if-then statement:
If a book is less than fifty years old, then it is unlawful to photocopy it without the publisher's permission.
Contrapositive:
If it is lawful to photocopy a book without the publisher's permission, then the book is at least fifty years old.

Conclusion of the passage:
Any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.
Rephrased as if IF-THEN statement:
If a book has been photocopied since 1978 without the publisher's permission, then it is at least fifty years old.
This conclusion is flawed in that it OMITS THE CONDITION ABOUT LAWFULNESS (highlighted above in green).

C: A driver who turns right must signal, so any driver who did not signal must not have turned right.
The blue premise in C, rephrased as an IF-THEN statement:
If a driver turns right, then it is unlawful for the driver not to signal.
Contrapositive:
If it is lawful for a driver not to signal, then the driver does not turn right.
The red conclusion in C, rephrased as an IF-THEN statement:
If a driver did not signal, then the driver did not turn right.
Like the conclusion of the passage, C's conclusion is flawed in that it omits the condition about lawfulness, highlighted above in green.
Thus, C exhibits a flaw similar to the one in the passage.



Many test-takers are drawn to A and D.

A: Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.
The blue premise in A, rephrased as an IF-THEN statement:
If something is a member of the solar system, then it is either a planet or a moon.
Contrapositive:
If something is neither a planet nor a moon, then it is not a member of the solar system.
Given this contrapositive, the green conclusion in A is valid.
Since A does not exhibit a flaw similar to the one in the passage, eliminate A.

D: Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.
The blue premise in D, rephrased as an IF-THEN statement:
If a person legally crosses a national boundary, then that person has a passport.
Contrapositive:
If a person does not have a passport, then that person does not legally cross a national boundary.
Given this contrapositive, the green conclusion in D is valid.
Since D does not exhibit a flaw similar to the one in the passage, eliminate D.
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
GMATNinja wrote:
anupam87 wrote:
Option A, C & D looked exactly identical to me.

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

Member of Solar System -> Planet or Moon
Neither Planet nor Moon -> Not a Member of Solar System (Contrapositive)

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.

Driver Turning Right -> Signal
No Signal -> Driver did not turn right (Contrapositive)

D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

Person Legally Crosses a boundary -> Passport
No Passport -> cannot legally cross a boundary (Contrapositive)

After reading all the posts I am still not convinced why should we reject A and D.
GMATNinja VeritasKarishma Could you please explain this question?

Is "the existence of a rule implies compliance with that rule" - the only factor differentiating correct and incorrect?

The most helpful first step in this situation is to identify the flaw in the reasoning given in the passage and then proceed to eliminate answers based on whether they exhibit a similar flaw. Consider the logic of the passage:

  • Copyright law, changed in 1978, now requires that books less than 50 years old must (LEGALLY) not be photocopied without permission.
  • Conclusion: Any book copied without permission since 1978 must (NECESSARILY) be at least 50 years old.

The argument assumes that because books less than 50 years old are not LEGALLY allowed to be photocopied, they NECESSARILY are not photocopied. But just because there is a man-made law prohibiting something does not mean that everyone follows that law. So, the logical error committed by the passage is assuming that the presence of a man-made law means that particular law is ALWAYS followed.

With that in mind, consider (A):

Quote:
(A) Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

(A) is tricky. The law under consideration is that every member of the solar system must (NECESSARILY, not legally) be a planet or moon. It then concludes that because an asteroid does not satisfy this condition, it is not a member of the solar system. (A) is incorrect because it confuses natural law with man-made law. Natural law is something that, according to science, NECESSARILY be followed. That’s different than saying something must LEGALLY be followed. For that reason, (A) does not contain the same logical error as the passage, and we can eliminate it.

Now here’s (C):

Quote:
(C) A driver who turns right must signal, so any driver who did not signal must not have turned right.

(C) first identifies a man-made law: any driver who turns right must (LEGALLY) signal. Then, it assumes that that law is always (NECESSARILY) followed: a driver who turns right ALWAYS signals and thus a driver who DOES NOT signal DID NOT turn right. This is precisely the same logical error (assuming that because something is LEGALLY required it is NECESSARILY required) as is committed in the passage. Let’s keep (C).

And here’s (D):

Quote:
(D) Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

Again, (D) first states a man-made law: legally crossing a national boundary requires a passport. But it does not assume that this law is ALWAYS followed. Instead, it suggests that to ignore this law is ILLEGAL. Because (D) qualifies its conclusion with the word “legally”, it allows for the possibility that people break the law (and cross national boundaries illegally) and thus does not commit the same logical error as the passage. Eliminate (D).

(C) is the best answer choice.

I hope that helps!


Hi GMATNinja! What is your take on B and E ?! Tks! :)
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
gmatt1476 wrote:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission. Thus, any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.

The reasoning above exhibits a flaw similar to one in which of the following?

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.
D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.


CR78561.01


Hi DmitryFarber! I know other tutors have engaged with this question, but it is still bugging me. Would you mind solving this question? Thank you! :please:
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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Quote:
Hi GMATNinja! What is your take on B and E ?! Tks! :)

Remember that once it's boiled way down, this argument amounts to: "because you're not supposed do X, no one did X." In other words, when a behavior is forbidden, people avoid that behavior. Simple enough.

Take another look at (B):
Quote:
Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.

If this option had said something like "because Demetrios didn't buy a bus pass he didn't ride the bus," well, that would work. We'd be concluding that because a behavior was forbidden, Demetrios didn't do it. But that's not what this says at all. There's nothing about behavior Demetrios is avoiding. So (B) is out.

Similar deal in (E):
Quote:
Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.

If this had something like "If Blodwen didn't pay state taxes, she must not be a state resident," we'd be in business. But again, that's not what we get here -- there's no behavior Blodwen is supposedly avoiding because it's forbidden. So (E) is gone too.

I hope that clears things up!
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
GMATIntensive wrote:
The Story

Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher’s permission. - In 1978 the copyright law was changed. Since then, books less than fifty years old may only be photocopied with the publisher’s permission.

Thus, any book that has been photocopied since 1978 without the publisher’s permission must be at least fifty years old - The author concludes that since the revised copyright law came into existence, the only books that have been photocopied must have been at least fifty years old.

Gist:
The modified copyright law restricts photocopying of recent books. Thus any books photocopied since the law change must not have been recent or the copiers must have got the publisher’s permission.

The Gap

Just ‘cause a law has been passed does not necessarily mean that everyone will follow it. The author, though, assumes that everyone follows the law and the only books that have been photocopied either were older than fifty years or were copied with the publisher’s permission.

The Goal

The basic flaw in the reasoning, as discussed above, is that the author assumes no one has broken the modified copyright law since it came into existence. We need to find an argument that has a similar flaw in reasoning.

The Evaluation

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.
Incorrect. This is a logical argument. Since any member must be a planet or a moon, if an asteroid is neither, it will not be a member. Since there is no flaw in the argument, this argument is not parallel to the one discussed above.

This is the first thing we recommend you do in a parallel argument question. Typically in such questions, the argument presented on top will have a flaw in reasoning. So, while going through the options, the first question to answer after understanding each option is: Is there even a flaw? If there isn’t one, we do not even need to bother figuring out whether the argument is parallel. A logical argument cannot be parallel to a flawed argument in terms of reasoning.

B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.
Incorrect. There is a flaw in this argument. The argument confuses a necessary condition (buying a bus pass to ride a city bus) for a sufficient condition. A bus pass is mandatory for riding a city bus. However, having a bus pass does not imply that someone must be riding a bus. One could very well have a bus pass and be sitting at home. While this argument is flawed, the flaw in reasoning is not similar to the flaw in the argument above. The argument on top is about the certainty of compliance just ‘cause there is a law. This one is about confusing a necessary condition for a sufficient one.

C. A driver who turns right must signal, so any driver who did not signal must not have turned right.
Correct. This argument makes the assumption that all drivers must be following the right turn signal rule. So, if a driver did not signal, it could not mean that he could have broken the rule and turned right without a signal; it must mean that the driver did not turn. This assumption is logically identical to the one made in the above argument. Both these arguments confuse the existence of a rule with conformity with the rule.

Here’s another parallel example: If you earn money above a minimum amount, you must pay taxes. So, anyone who did not pay taxes must not have earned money above that minimum amount.

Clearly, the author does not know of tax evasion.

D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.
Incorrect. The option does not say that anyone who does not have a passport cannot cross a national boundary. It says that someone like that cannot ‘legally’ cross a national boundary. That is actually logical. This is a logical argument. So as discussed in option A, since there is no flaw in the argument, this argument is not parallel to the one given in the passage.

What if we were to remove the word “legally” from this option? Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary. Is there a flaw in this reasoning? If so, is it similar to the one in the passage?

E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.
Incorrect. This option also confuses a necessary condition for a sufficient one. It is necessary for wage earners in the state to pay state taxes. Doesn’t mean they are the only ones who pay state taxes. There could be other states as well that require their wage-earning residents to pay state taxes. This option is also flawed. However, the flaw is similar to the one we saw in option B, and not similar to the flaw we observe in the copyright law argument.


If you have any doubts regarding any part of this solution, please feel free to ask.



Hey GMATIntensive ChiranjeevSingh Can you help explain this part?

What if we were to remove the word “legally” from this option? Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary. Is there a flaw in this reasoning? If so, is it similar to the one in the passage?

According to me, if we were to remove 'Legally' from the option, the argument would not have a logical flaw per-se. Unless, we assume that the statement 'Anyone who crosses a national boundary must have a passport' implies that its a law.
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
GMATGuruNY wrote:
The contrapositive of IF A, THEN B is IF NOT B, THEN NOT A.
If an IF-THEN statement is true, its contrapositive is also true.
True IF-THEN statement:
If John is in Times Square, then John is in New York.
Contrapositive:
If John is not in New York, then John is not in Times Square.

gmatt1476 wrote:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission. Thus, any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.

The reasoning above exhibits a flaw similar to one in which of the following?

A. Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.
B. Anyone who rides a city bus must buy a bus pass, and since Demetrios has a bus pass, he must be riding on a city bus.
C. A driver who turns right must signal, so any driver who did not signal must not have turned right.
D. Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.
E. Any wage earner residing in the state must pay state taxes, so since Blodwen pays state taxes, she must be resident in the state.


CR78561.01


Premise of the passage:
Since 1978 when the copyright law was changed, books that are less than fifty years old must not be photocopied without the publisher's permission.
Rephrased as an if-then statement:
If a book is less than fifty years old, then it is unlawful to photocopy it without the publisher's permission.
Contrapositive:
If it is lawful to photocopy a book without the publisher's permission, then the book is at least fifty years old.

Conclusion of the passage:
Any book that has been photocopied since 1978 without the publisher's permission must be at least fifty years old.
Rephrased as if IF-THEN statement:
If a book has been photocopied since 1978 without the publisher's permission, then it is at least fifty years old.
This conclusion is flawed in that it OMITS THE CONDITION ABOUT LAWFULNESS (highlighted above in green).

C: A driver who turns right must signal, so any driver who did not signal must not have turned right.
The blue premise in C, rephrased as an IF-THEN statement:
If a driver turns right, then it is unlawful for the driver not to signal.
Contrapositive:
If it is lawful for a driver not to signal, then the driver does not turn right.
The red conclusion in C, rephrased as an IF-THEN statement:
If a driver did not signal, then the driver did not turn right.
Like the conclusion of the passage, C's conclusion is flawed in that it omits the condition about lawfulness, highlighted above in green.
Thus, C exhibits a flaw similar to the one in the passage.



Many test-takers are drawn to A and D.

A: Any member of the solar system must be either a planet or a moon, so if an asteroid is neither a planet nor a moon, it must not be a member of the solar system.
The blue premise in A, rephrased as an IF-THEN statement:
If something is a member of the solar system, then it is either a planet or a moon.
Contrapositive:
If something is neither a planet nor a moon, then it is not a member of the solar system.
Given this contrapositive, the green conclusion in A is valid.
Since A does not exhibit a flaw similar to the one in the passage, eliminate A.

D: Anyone who legally crosses a national boundary must have a passport; thus anyone who does not have a passport cannot legally cross a national boundary.
The blue premise in D, rephrased as an IF-THEN statement:
If a person legally crosses a national boundary, then that person has a passport.
Contrapositive:
If a person does not have a passport, then that person does not legally cross a national boundary.
Given this contrapositive, the green conclusion in D is valid.
Since D does not exhibit a flaw similar to the one in the passage, eliminate D.



When you are writing the contrapositive, how do you know that "unlawful" must be flipped to "lawful"? How do you know that "without" must not be flipped to "with"?

Also are there any good books that talk about conditional reasoning and causal reasoning in depth? I read the PowerScore CR Bible, and while it provides helpful tools to analyze simple conditional statements, I am unable to understand what the sufficient and necessary conditions are for more complex questions that involve multiple words such as "unless", "without", "must", etc.
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Re: Since 1978 when the copyright law was changed, books that are less tha [#permalink]
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