C If x and y are positive integers, Q: is x + y^2 odd?
(1) y is odd. NOT Sufficient y has no factor of 2, therefore y^2 also has no factor of 2. Without knowing x, we can’t answer the question. The data is NOT Sufficient.
If x is even, and we add an odd number, the outcome is odd. If x is odd and we add an odd number, the outcome is even. Without knowing x, we can’t answer the question. The data is NOT Sufficient.
(2) x is odd. If y is even (has a factor of 2) then y^2 is even. If this is so, then x + y^2 IS odd, but we do not know this. If y is odd (has no factor of 2), then this sum is even.
Without knowing y, we can’t answer the question. The data is NOT Sufficient.
NOT Sufficient
TOGETHER: y is odd (no factor of 2 in y^2) so y^2 is odd too.
x is odd.
ODD plus ODD = EVEN.
There IS enough information to answer the question. The answer happens to be “NO!”, but the data Is SUFFICIENT!!