Simplifying fractions is important. You could go into a cake shop and ask for 50/200 of a cake, but you'd probably get a funny look!
50/200 is, of course, the same as a quarter! Let's see why:
Next, and this can be tricky (know your times tables!), we have to see if the top and bottom number have a common factor.
In this case, both 5 and 20 have 5 as a factor: so we can divide top and bottom by 5... giving 1/4 as the simplest fraction.
Simplifying fractions is sometimes called cancelling down.