m13 #13 The unlucky 13!

Is \((x - y)*(x + y)\) an even integer?

1. \(x\) and \(y\) are integers
2. \(x + y\) is even

Chose incorrect B and after looking at the solution thought of adding a little to OE (don't know if it is a superstition, but I'm getting #13 wrong in so many tests :evil: )...

x+y is even

in case both are integers, then they are either both odd or both even => x-y will be even.

in case both are fraction (if only 1 is fraction, then "x+y is even" does not holds true). Check it with few substitutions for odd/even combination on denominator so as to keep x+y even:
Even denominator... 1/2+3/2 => subtraction result odd. But overall result even.
Odd denominator... 5/3+1/3 => subtraction result is fraction making B false
So they have to be integers OA