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

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Manager
Joined: 23 Apr 2007
Posts: 135

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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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24 Jun 2007, 07:21
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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.

Could someone please explain why C is the ans?
coz if not D, then it could be B or C and that means it could be A!

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Manager
Joined: 23 Dec 2006
Posts: 134

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24 Jun 2007, 07:53
This is a case when an understanding of formal logic would come in handy. I don't understand it that well myself, but it's a rule that I've learned:

If we have: If A, then B

The only thing we can infer from this is: If Not B, then Not A

C satifies this condition.

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Director
Joined: 30 Nov 2006
Posts: 590

Kudos [?]: 320 [0], given: 0

Location: Kuwait

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24 Jun 2007, 08:17
For events and causations in general, define events x and y.

If X --> Y, this implies three things:

o Y --/-> X
o Z --/-> Y
o No Y, then No X

The third point resides on the reasoning that Y is always a result of event X, and thus if no Y is showing, then X must have NOT happened.

Now, to out question: if not D, then not C; if not C, then not B; if not B, then not A. Therefore, if not D then not A

Kudos [?]: 320 [0], given: 0

24 Jun 2007, 08:17
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# If A, then B If B, then C. If C, then D. If all of the

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