Question on numbers

[srn]

If x and y are positive integers, is the product xy even?

a. 5x-4y is even.
b.6x+7y is even.

ans -d

Please explain how you came to the conclusion.

[moutar]

5x - 4y is even implies that 5x is even (4y is even and even - even equals even). If 5x is even, x is even and therefore xy is even. SUFFICIENT

6x+7y is even implies that 7y is even (6x is even and even+even=even). If 7y is even, then y is even and therefore xy is even. SUFFICIENT

Therefore D. Each statement alone is sufficient.

[cubicle_bound_misfit]

more algebra wise,

5x -4y =2k

5x = 4y+2k .... even

hence x is even hence xy is even...

same approach for stmt 2.