Why does two odd numbers equal an even number?

Answer 1

Suppose x and y are two odd numbers.Then x = 2m - 1 and y = 2n - 1 for some integers m and n.

Then x + y = m2 - 1 + 2n - 1 = 2m + 2n - 2 = 2(m + n - 1)

That is, x + y is a multiple of 2: in other words, it is even.