If z is a positive number, is z an even integer?
(1) 3z is an even integer.
(2) 5z is an even integer.
Statement 1: 3z is even.
It's possible that z = 2, which is an even integer.
It's possible that z = 2/3, which is not an even integer.
INSUFFICIENT.
Statement 2: 5z is even.
It's possible that z = 2, which is an even integer.
It's possible that z = 2/5, which is not an even integer.
INSUFFICIENT.
Every test-taker should know the following:
EVEN - EVEN = EVEN.
Statements 1 and 2 combined:
Here, 5z is even and 3z is even.
Thus:
5z-3z = even - even = even.
Since 5z-3z = 2z, 2z must be even.
Since 3z is even and 2z is even, we get:
3z-2z = even - even = even.
Since 3z-2z = z, z must be even.
SUFFICIENT.
The correct answer is
C.
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