What are 5 minutes as a fraction of one hour?

First, you need to make the units the same. 

We need to work out how many minutes there are in 1 hour.

There are 60 minutes in one hour.

Let's try another. 

Write 12 metres as a fraction of 1 km.
Again, first, we need to make sure the units are the same.

There are 1000 m in 1 km.