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# If A, then B. If B, then C. If C, then D. If all of the

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If A, then B. If B, then C. If C, then D. If all of the [#permalink]

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17 Aug 2011, 03:45
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If A, then B.
If B, then C.
If C, then D.
If all of the statements above are true, which of the following must also be true?
(A) If D, then A.
(B) If not B, then not C.
(C) If not D, then not A.
(D) If D, then E.
(E) If not A, then not D.

[Reveal] Spoiler:
I chose B. But OA is C. How?
[Reveal] Spoiler: OA

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17 Aug 2011, 03:56
there are rules that concern negative and positive IF X THEN Y IF NOT X THEN NOT Y ETC..:
if A then B means that if B did not happen than A did not happen. so: IF D not then C not. if C not then B not. if B not then A not. so if D not then not C,B or A.

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17 Aug 2011, 04:02
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If A, then B.
If B, then C.
If C, then D.
If all of the statements above are true, which of the following must also be true?
(A) If D, then A.
(B) If not B, then not C.
(C) If not D, then not A.
(D) If D, then E.
(E) If not A, then not D.

I saw the OA in the mail but C does make sense.

(A) If D, then A
A will definitely result in D doesn't mean someone else can't trigger D. Maybe Z can spawn D. So, we can have D by Z. A is nowhere in the picture.

(B) If not B, then not C.
Same logic as before. C is triggered by B doesn't mean ONLY B can trigger C. GHOST may trigger C. So, we have GHOST and C., and no B. This becomes false.

(C) If not D, then not A.
Definitely true. If we don't see D, it means there CAN't be A. Know this. As soon as A appears, at least B,C,D also appear. Thus, if don't see D, there can't be any A. However, if we see D, there is no guarantee that A is there. CORRECT.

(D) If D, then E.
What is E.

(E)If not A, then not D.
As I said in option "C", D can be spawned by something else. Say GHOST->C->D
Not true.

Ans: "C"
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17 Aug 2011, 05:32
ok here's a simpler way, if you are good with quant inequalities

if A -- > B, if B -- C , If C -- >

which implies if A -- > D

if you negate, then it becomes the opposite ~D -- > ~A which is C
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17 Aug 2011, 05:47
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viks4gmat wrote:
ok here's a simpler way, if you are good with quant inequalities

if A -- > B, if B -- C , If C -- >

which implies if A -- > D

if you negate, then it becomes the opposite ~D -- > ~A which is C

well i love the Qyant approach: did you mean to say something like:

IF (POSITIVE) A>B>C>D THEN THE IF NOT (NEGATIVE) WILL BE LIKE MULTIPLYING BY -(1) WHICH REVERSES THE INEQUALITY TO IF NOT D>NOT C> NOT B> NOT A
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17 Aug 2011, 21:20
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dimri10 wrote:
viks4gmat wrote:
ok here's a simpler way, if you are good with quant inequalities

if A -- > B, if B -- C , If C -- >

which implies if A -- > D

if you negate, then it becomes the opposite ~D -- > ~A which is C

well i love the Qyant approach: did you mean to say something like:

IF (POSITIVE) A>B>C>D THEN THE IF NOT (NEGATIVE) WILL BE LIKE MULTIPLYING BY -(1) WHICH REVERSES THE INEQUALITY TO IF NOT D>NOT C> NOT B> NOT A

yup thats pretty much what i intend to say !!!

if A> B> C > D then negating/ NOT-ing the components simply changes the direction of the sign
-A < -B < -C < -D (or -D> -C > -B > -A whichever way you are comfortable reading the equation from )
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07 Sep 2011, 06:09
good question. i have an even better trick for such questions. i solved the question in 1:17; i could've done that even earlier. here's the trick.

a->b

to find what else can be true, reverse the order of a,b and make them logical negations of themselves.

a->b= b'->a'
"if A, then B" = "if not B, then not A"

e.g. if it is cloudy, it will rain.
if it is not cloudy, then it will not rain (incorrect. we're not sure)
if it is raining, then it is cloudy (incorrect. again may be it also rains when there are no clouds. we don't know)

if it is not raining, then it is not cloudy (bingo! correct ans)
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07 Sep 2011, 17:37
If A, then B.
If B, then C.
If C, then D.
If all of the statements above are true, which of the following must also be true?
(A) If D, then A.If D, that means A already happened. Not the other way
(B) If not B, then not C.If B, then C. If not B, we have no idea about C or D except A.
(C) If not D, then not A.True. If not D, then not C, not B and not A.
(D) If D, then E.Irrelevant. E is not in the question
(E) If not A, then not D.If not A, we have no idea about B, C or E

[Reveal] Spoiler:
I chose B. But OA is C. How?

So C.
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10 Sep 2011, 01:24
C
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10 Sep 2011, 05:41
Good question. I got it wrong...
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01 Oct 2011, 02:51
32 sec. straight forward C

A-B-c-d

xd-xa.( x-mean not )
I don't know how to express exact symbol
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04 Oct 2011, 18:02
Tricky one.. Looking at the inverse relationship the ans would be C.
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05 Nov 2011, 09:06
Pls explain. By the same logic even A is true.

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05 Nov 2011, 18:47
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Re: If A, then B. If B, then C. If C, then D. If all of the [#permalink]

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08 Nov 2011, 09:03
http://en.wikipedia.org/wiki/Contraposition
A => B is same as ~B=>~A

So ~D => ~C => ~B => ~A
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Re: If A, then B. If B, then C. If C, then D. If all of the [#permalink]

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30 May 2015, 21:02
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Re: If A, then B. If B, then C. If C, then D. If all of the [#permalink]

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01 Jun 2015, 23:11
C
D or for that matter any other resulting one (B,C,D) can exist without the cause also bc the argument only says that if A, B,C exists then will B,C,D exist respectively. reverse is not true there can be other causes too leading to the result.
Thus we can say that no result means no cause ---- right
and not that no cause means no result as result might exist bc of other causes too
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Re: If A, then B. If B, then C. If C, then D. If all of the [#permalink]

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20 Jan 2016, 09:29
viks4gmat wrote:
dimri10 wrote:
viks4gmat wrote:
ok here's a simpler way, if you are good with quant inequalities

if A -- > B, if B -- C , If C -- >

which implies if A -- > D

if you negate, then it becomes the opposite ~D -- > ~A which is C

well i love the Qyant approach: did you mean to say something like:

IF (POSITIVE) A>B>C>D THEN THE IF NOT (NEGATIVE) WILL BE LIKE MULTIPLYING BY -(1) WHICH REVERSES THE INEQUALITY TO IF NOT D>NOT C> NOT B> NOT A

yup thats pretty much what i intend to say !!!

if A> B> C > D then negating/ NOT-ing the components simply changes the direction of the sign
-A < -B < -C < -D (or -D> -C > -B > -A whichever way you are comfortable reading the equation from )

Awesome -
Inequality to cause and effect ....
Struggling with "cause and effect"questions....Please have a look at the approach
Re: If A, then B. If B, then C. If C, then D. If all of the   [#permalink] 20 Jan 2016, 09:29
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