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CR question

by gmatmillenium » Tue Apr 27, 2010 6:12 pm
Can someone please explain the logic behind the answer for this?

If W, then X
If X, then Y
If Y, then Z

Which of the following must be true?

Ans is : If not Z, then not W
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by tpr-becky » Tue Apr 27, 2010 7:26 pm
For if W then X the only two things we know are that if we have W then we will have X and alternately if we don't have X that means we don't have W.

For example - if we are in Washington DC THEN we are in the U.S. so if we look around and see we are in Washington we know that we are in the US. if we are anywhere else we can't be sure. BUT if we know that we are not in the U.S. then we know we cannot be in Washington.

Your question leads from one to the next - so ifW then X then Y then Z - so we can take out the middle men and say if W then Z. and by the reasoning above if not Z then not W.

Hope that helps.
Becky
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by gmatmillenium » Tue Apr 27, 2010 8:58 pm
tpr-becky wrote:For if W then X the only two things we know are that if we have W then we will have X and alternately if we don't have X that means we don't have W.

For example - if we are in Washington DC THEN we are in the U.S. so if we look around and see we are in Washington we know that we are in the US. if we are anywhere else we can't be sure. BUT if we know that we are not in the U.S. then we know we cannot be in Washington.

Your question leads from one to the next - so ifW then X then Y then Z - so we can take out the middle men and say if W then Z. and by the reasoning above if not Z then not W.

Hope that helps.

Becky

Thanks...I was looking exactly for the kind of clue that you provided to solve this...

If Washington, then USA,
If USA, then North America
If North America, then Americas

lot simpler to answer this way....subset/superset
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