Pattern - Even and Odd

The most common use of modulo is checking if a number is even or odd. If $n \bmod 2 = 0$, then $n$ is even. If $n \bmod 2 = 1$, then $n$ is odd.

For example, $8 \bmod 2 = 0$ (even) and $7 \bmod 2 = 1$ (odd). This works because even numbers are exactly those divisible by $2$.

You'll use this pattern constantly. Any time you need to alternate behavior or split items into two groups, modulo 2 is your tool.