To see why, consider two numbers \(a\) and \(b\) which are congruent modulo \(n\text{.}\) Then \(a\) and \(b\) have the same remainder when divided by \(n\text{.}\) We have
\begin{equation*}
a = q_1 n + r \qquad\qquad b = q_2 n + r\text{.}
\end{equation*}