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MGMAT question.

by simplyjat » Wed Apr 02, 2008 9:04 am
This is a question for mgmat. For which I do not agree with the explanation. What do you guys say...

Is z even?
(1) z/2 is even.
(2) 3z is even.


Moderator, if it is not OK to post mgat questions here, kindly delete the post.
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Re: MGMAT question.

by Stuart@KaplanGMAT » Wed Apr 02, 2008 11:32 am
simplyjat wrote:This is a question for mgmat. For which I do not agree with the explanation. What do you guys say...

Is z even?
(1) z/2 is even.
(2) 3z is even.


Moderator, if it is not OK to post mgat questions here, kindly delete the post.
(1) z/2 = even

Like any other equation, we can manipulate this to:

z = 2*even

Well, 2 times any integer will be even, therefore z will always be even: sufficient.

(2) 3z = even.

z = even/3

Will all even numbers divided by 3 be even? No. Will some of them be even? yes.

For example, we could have picked:

z = 6/3 = 2. Is 2 even? Yes.

or

z = 4/3 = 1.333. Is 1.333 even? No.

Since we can get a "yes" and a "no" answer, (2) is insufficient.

(1) is sufficient, (2) is insufficient: choose (A).

* * *

If you chose (D), both sufficient, you probably made the erroneous assumption that z had to be an integer. However, since we're never told that z must be an integer, we can't preclude other possibilities.
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