Textbook Problem

In each of 3-6, the relation R is an equivalence relation on A. As in Example 8.3.5, first find the specified equaivalence classes. Then state the number of distinct equivalenvce classes for R and list them.

$A=\left\{1,2,3,4,\mathrm{...},20\right\}.$R is defined on A as folloes:

$\text{For}\text{all}x,y\in A,xRy\iff 4|\left(x-y\right)$

Equivalence classes:[1], [2], [3], [4], [5].