How to prove that if $7n - 5$ is odd, then $n$ is even?

Question

How to prove that

If $7n - 5$ is odd, then $n$ is even?

Answer 1

Suppose by way of contradiction that $n$ were odd. Then $7n$ is odd so $7n-5$ is even. Thus, $n$ must be even.

Answer 2

Consider this modulo $2$. If $7n-5=1$, then $n=7n=5+1=0$ over $\mathbb{Z}/2$.