Madelaine88 wrote:
If positive integers x and y are not both odd, which of the following must be even?
a/ xy
b/ x+y
c/ x-y
d/ x+y-1
e/ 2(x+y)-1
Why x+y/x-y can`t be even?
fluke, I think Madelaine was asking why x+y or x-y is not the correct answer here (I don't think the question was about division, since (x+y)/(x-y) is not among the answer choices). It's vital here to note that the question asks "which of the following *must* be even". That's a very different question from "which of the following *could* be even". Certainly x+y *could* be even, if x and y are both even, but if, say, x is even and y is odd, then x+y will be odd. So x+y does not need to be even, and B is thus not the right answer here. But if at least one of x or y is even, then xy will always be even, so the answer is A.
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