Baten80 wrote:

If x, y and z are positive integers, is x - y odd?

(1) x=z^2

(2) y=(z-1)^2

Can this problem be solve by plunging number?

Yes, you can plug in numbers. Generally, in even odd questions, plugging numbers works. (mind you, generally, not always)

Break it down in the following way:

If x, y and z are positive integers, is x - y odd?

Question: Is one of x and y even and one odd? (because x - y will be odd only if one of them is even and one is odd)

(1) x=z^2

If z is even, x is even. If z is odd, x is odd. No info about y.

or if z = 2, x is 4. If z = 1, x is 1.

(2) y=(z-1)^2

If z is even, y is odd. If z is odd, y is even. No info about x.

or If z = 2, y = 1. If z = 1, y is 0 (even number).

Together:

If z is even, x is even and y is odd.

If z is odd, x is odd and y is even.

One is always odd, other is always even.

or

If z is 2, x = 4 and y = 1

If z = 1, x = 1 and y = 0

Answer (C)

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