[Math] Find when three numbers have the same remainder when divided by the same number

elementary-number-theory

If three numbers 112, 232, and 400 are each divided by the number D, each of their quotients will have the same remainder R. Find R where R>1

How should I approach this?

Best Answer

Hint: $$112 - R \equiv 0 \mod D$$

$$232 - R \equiv 0 \mod D$$

$$400 - R \equiv 0 \mod D$$

$$120 \equiv 0 \mod D$$ $$168 \equiv 0 \mod D$$

Hence $D$ is a common factor of both $120$ and $168$.

$$24 \equiv 0 \mod D$$

$D \in \{1,2,3,4,6,8,12,24 \}$

Use $R>1$ to identify which $D$ is possible.