Is z an even integer?

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by Jay@ManhattanReview » Tue Aug 21, 2018 12:17 am

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BTGmoderatorDC wrote:Is z an even integer?

(1) z/2 is an even integer.
(2) 3z is an even integer.

OA A

Source: Manhattan GMAT
Let's take each statement one by one.

(1) z/2 is an even integer.

z/2 = Even
=> z = 2*Even
=> z = Even*Even = Even

The answer is Yes. Sufficient.

(2) 3z is an even integer.

=> 3z = Even
z = Even/3

Case 1: Say "Even = 6," then z = 6/3 = 2, an even integer. The answer is Yes.
Case 2: Say "Even = 2," then z = 2/3, not an integer. The answer is No. Insufficient

Note that it is not to be assumed that z is an integer.

The correct answer: A

Hope this helps!

-Jay
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by GMATGuruNY » Tue Aug 21, 2018 3:15 am

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BTGmoderatorDC wrote:Is z an even integer?

(1) z/2 is an even integer.
(2) 3z is an even integer.
Statement 1:
Make a list of options for z/2:
z/2 = 0, 2, 4, 6, 8...
To get a list of options for z, multiply every value by 2:
z = 0, 4, 8, 12, 16...
In every case, z is an even integer, so the answer to the question stem is YES.
SUFFICIENT.

Statement 2:
Make a list of options for 3z:
3z = 0, 2, 4, 6, 8...
To get a list of options for z, divide every value by 3:
z = 0, 2/3, 4/3, 2, 8/3...
If z=0, then z is an even integer, so the answer to the question stem is YES.
If z=2/3, then z is NOT an even integer, so the answer to the question stem is NO.
INSUFFICIENT.

The correct answer is A.
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