4/5 of the cake was left but brain ate some and then 1/4 was left how much did brain eat?

11/20

Step-by-step explanation:

We can visualize the cake as being something that has a mass. Let's say the mass of the cake is 100g.

4/5 was left, this means 4/5 of 100 was left which is 80g

Now, brain ate some leaving 1/4 of the cake. This means what was left is 1/4 of 100 = 25g

Now, we know that brain ate from 80g to 25g. The amount ate by brain is 80g - 25g = 55g

Now, the fraction ate by brain is 55/100 = 11/20