Scale Drawings of a map

Question

The question: The scale on a map is given as $1:40000$. If the actual distance between two ships is $9$km, what is their distance on the map?

I tried dividing $40000$ with $100$ but I'm not sure if it's right.

Answer 1

Each length on the map is $\frac1{40000\text{th}}$ of that in real life.
So for $9$km, it is represented on the map by a length $\frac1{40000\text{th}}$ of $9$km.
$9$km is $9000000$mm.
Therefore the length is $\frac{9000000\text{mm}}{40000}=225$mm.