Can someone please explain me how the given answer is true

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[email protected]: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sat Mar 26, 2011 12:54 pm

by [email protected] » Mon Apr 25, 2011 6:55 pm

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.

Given answer is C,but I don't understand how it is C. I would rather go with E.

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Source: Beat The GMAT — Critical Reasoning | Mon Apr 25, 2011 6:55 pm

vineeshp: Legendary Member; Posts: 965; Joined: Thu Jan 28, 2010 12:52 amFollowed by: 34 members; Thanked: 156 times; GMAT Score:720

by vineeshp » Mon Apr 25, 2011 8:23 pm

I dont think GMAT ever asks such questions. it does not clearly say what the circumstances are. So such questions should be avoided.

From your question, we can infer that If A then D.
But it only means that if A happens, then D can happen.
It does not in any place suggest that A is the only way of making D happen.
(If you win, I will give you a treat. This does not mean that if you dont win, there is no chance of me giving you treat. I can give you another treat, say, if i score 760 on the GMAT.)

So E is wrong.

But now with C. It says if not D then not A.
Which means D did not happen. We know that D happens if C, C if B and B is A. So if not D, then A dint happen.

Vineesh,
Just telling you what I know and think. I am not the expert.

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rohu27: Legendary Member; Posts: 586; Joined: Tue Jan 19, 2010 4:38 amFollowed by: 5 members; Thanked: 31 times; GMAT Score:730

by rohu27 » Mon Apr 25, 2011 8:32 pm

IMO questions wth heavy formal logic are not expected on GMAT(an advice frm an expert too few days back in this forum).

but i still tried this Q

A)- Q only says if C occurs D occurs but C is not the only way, there may well be others too
B)-if not B then not A is correct, cant say abt C
C) - if not D->not C->notB->notA
D)no mention of E
E)same logic as A

HTH
Cheers,

Have time? https://www.beatthegmat.com/730-q-50-v40 ... 88058.html

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[email protected]: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sat Mar 26, 2011 12:54 pm

by [email protected] » Tue Apr 26, 2011 4:44 am

Thank you both for your response.

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atulmangal: Legendary Member; Posts: 1112; Joined: Sat Feb 26, 2011 11:16 amFollowed by: 49 members; Thanked: 77 times

by atulmangal » Tue Apr 26, 2011 7:04 am

Hi,

This is based on a simple concept: the concept is

So if X -> Y then the following conclusions are wrong:

Y -> X
X (NOT) -> Y (NOT)

Only the following conclusion is right:

Y (not) -> X (not)

In your question,

we get, A -> B -> C -> D => A -> D

Hence from u can state that D(NOT) -> A(NOT)

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