Powerscore Test 2 Question #11 (odd/even)

[dddannie6]

If x and y are integers and x=50y+69, which of the following must be odd?

xy
x+y
x+2y
3x-1
3x+1

I choose the correct answer which was x+2y
but I cannot seem to understand why that is since when I choose numbers both b and c are coming up with odd answers.

Please help!

Best,
Dannie

[tommywallach]

Hey Dannie,

It's not enough to choose one set of numbers, if you want to know something definitively. You could do this conceptually:

Based on the information, x will be odd, and we have no idea what y will be.

(A) odd * odd = odd, odd * even = even, so who knows?
(B) odd + odd = even, odd + even = even, so who knows?
(C) odd + even = odd, DONE!
(D) 3 * odd - 1 = even, no good!
(E) 3 * odd + 1 = even, no good!

Make sense?

-t