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For a certain set of numbers, if x is in the set, then x - 3

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For a certain set of numbers, if x is in the set, then x - 3 [#permalink] New post 30 Jul 2012, 06:45
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For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4
b) -1
c) -5

A. a only,
B. b only,
C. c only,
D. a and b only
E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer :? )
[Reveal] Spoiler: OA

Last edited by Bunuel on 30 Jul 2012, 06:54, edited 2 times in total.
Renamed the topic.
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Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink] New post 30 Jul 2012, 07:02
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jayoptimist wrote:
For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4
b) -1
c) -5

A. a only,
B. b only,
C. c only,
D. a and b only
E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer :? )


Notice that the question asks which of the following MUST be in the set, not COULD be in the set.

Since 1 is in the set, then so must be 1-3=-2. Similarly, since -2 is in the set, then so must be -2-3=-5. Could 4 and -1 be in the set? Certainly, but we don't know that for sure.

Answer: C.

Regarding your question: we don't know which is the source integer in the set, if it's 1, then 4 won't be in the set but if the source integer is say 7, then 4 will be in the set. So, 4 may or may not be in the set.

Similar questions to practice:
a-set-of-numbers-has-the-property-that-for-any-number-t-in-t-98829.html
k-is-a-set-of-integers-such-that-if-the-integer-r-is-in-k-103005.html

P.S. Please read and follow: rules-for-posting-please-read-this-before-posting-133935.html (rule #3).
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For a certain set of numbers, if x is in the set, x-3 is als [#permalink] New post 30 Dec 2012, 16:22
For a certain set of numbers, if x is in the set, x-3 is also in the set. If the number 1 is in the set, which of the following must also be in the set
I) 4
II) -1
III) -5

the answer is III only, means -5.

They are reasoning that, 1 in the set, so -2 also in the set, so -5 also in the set, so -8 also in the set.

I wonder why 4 can't be in the set??? let consider 1 is x-3, not x, hence x = 4.
What is the trap of GMAT here?

(I always have problem with the trap of gmat)
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Re: For a certain set of numbers, if x is in the set, x-3 is als [#permalink] New post 30 Dec 2012, 20:40
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akhandamandala wrote:
For a certain set of numbers, if x is in the set, x-3 is also in the set. If the number 1 is in the set, which of the following must also be in the set
I) 4
II) -1
III) -5

the answer is III only, means -5.

They are reasoning that, 1 in the set, so -2 also in the set, so -5 also in the set, so -8 also in the set.

I wonder why 4 can't be in the set??? let consider 1 is x-3, not x, hence x = 4.
What is the trap of GMAT here?

(I always have problem with the trap of gmat)


We can look at this as a cause and effect problem. "x" is the cause and "x-3" is the effect. i.e. We are given that is "x" is in the set "x-3" is also in the set. The reverse need not necessarily be true. We cannot take the effect to be the cause.
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Re: For a certain set of numbers, if x is in the set, x-3 is als [#permalink] New post 31 Dec 2012, 02:06
Expert's post
akhandamandala wrote:
For a certain set of numbers, if x is in the set, x-3 is also in the set. If the number 1 is in the set, which of the following must also be in the set
I) 4
II) -1
III) -5

the answer is III only, means -5.

They are reasoning that, 1 in the set, so -2 also in the set, so -5 also in the set, so -8 also in the set.

I wonder why 4 can't be in the set??? let consider 1 is x-3, not x, hence x = 4.
What is the trap of GMAT here?

(I always have problem with the trap of gmat)


Merging similar topics. Please refer to the solutions above.
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COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink] New post 31 Dec 2012, 11:11
great!!!, thanks guys :-D
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Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink] New post 31 Dec 2012, 11:21
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jayoptimist wrote:
For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4
b) -1
c) -5

A. a only,
B. b only,
C. c only,
D. a and b only
E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer :? )


I call them Verbal diaorea of GMAT. You have to follow these verbal vomits carefully. When they say x-3 is there only x-3 is guaranteed to be there nothing else. And so here you can not travel to the side of the stream.
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Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink] New post 31 Dec 2012, 16:56
maibhihun wrote:
jayoptimist wrote:
For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4
b) -1
c) -5

A. a only,
B. b only,
C. c only,
D. a and b only
E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer :? )


I call them Verbal diaorea of GMAT. You have to follow these verbal vomits carefully. When they say x-3 is there only x-3 is guaranteed to be there nothing else. And so here you can not travel to the side of the stream.


that's true, I have no problem with math, but I have quite problem with those kinds of "Verbal diaorea of GMAT". Hope exercises will help much. Thanks
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Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink] New post 03 Mar 2014, 11:47
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Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink] New post 27 Apr 2014, 08:18
It does not make logical sense to only have -5 and 4 is not the correct answer.

Can't we take that 1 is the result of X -3 ? In which case, X = 4.

I cant agree with -5 more because it is one more "jump"

X = 1 .... 2nd number is ( -2 ) is fine with me.
But the question did not say that "X - 6" also exists? Because X is still 1, and did not "move on" to become -2.

Agree its a bit of a "throw you off if you did not buy our official guide" even if you had maths as your bach degree.

Hope this kind of stuff don't pop up for my coming exam, but it cant be helped =)
Re: For a certain set of numbers, if x is in the set, then x - 3   [#permalink] 27 Apr 2014, 08:18
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