In $\mathbb{Z}_8$, the residue classes modulo 8 written $[0]$ to $[7]$, what is $[5] + [6]$?

Explanation

1. 01

   $[a] + [b] = [a + b]$, reduced modulo 8.

2. 02

   $5 + 6 = 11 \equiv 3$, so the sum is $[3]$.