How much is the difference between 9 out of 10 and 4 out of 5 more than 1 out of 5?

How much is the difference between 9 out of 10 and 4 out of 5 more than 1 out of 5?

(9/10-4/5)-(1/5)×(1/5)
=1/10-1/25
=3/50