Question

50% of all cakes baked that week were party cakes, 1/5 were fruit cakes and the remainder were sponge cakes.

what percentage of cakes were sponge cakes

Answer 1

50% = 1/2 party cakes
1/5= 20% fruit cakes
x=sponge cakes

50%+20%+x=100%
x = 100%-50%-20%
x=30%.

Answer 2

In this case the best way to approach this is to turn one into a percentage, as this will make it easier. As you've got 1/5, turning this into a percentage will be 20%. Then simply add 50% and 20% together, giving you 70%, and subtracting this from 100%, giving you 30%. 30% of the cakes made were sponge cakes