smc

Let $a$ be the bigger number and $b$ be the smaller. $a+b=5(a-b)$. Multiplying out gives $a+b=5a-5b$ and rearranging gives $4a=6b$ and factorised into $2a=3b$ and then solving gives $\frac{a}{b}=\frac{3}{2}$, so the answer is $\boxed{\frac{3}{2}}$.