Definitions:
A number, x, is even if it satisfies: x = 2n for some integer n
A number, x, is odd if it satisfies: x = 2k+1 for some integer k
Rewriting the Question:
In this case the question is asking if there is a number, x, that is has the following property:
x = 2n for some integer n AND x = 2k+1 for some integer k
Proof:
We can set these two equations equal:
2n = x = 2k + 1
2n = 2k + 1
2n - 2k = 1
2(n - k) = 1
Let number y = n - k. Note that since n and k are integers, n-k (and therefore, y) must also be an integer.
2y = 1
You can see on the left side (2y) that this becomes the definition of an even number! So the left side is an even number and the right side is 1. Since we know by definition that 1 is not an even number and k must be an integer (not 0.5), this equation becomes false.
As a result, there are NO numbers that can be both even AND odd.
