the total percentage is 100 %
there are party cakes, fruit cakes and sponge cakes
50 % of the cakes are party cakes
1/5th of the cakes are fruit cakes.
so 1/5th of 100 % is -
= 20%
therefore 20 % of the cakes are fruit cakes
remainder of the cakes were sponge cakes
the sum of the party and fruit cakes are - 50 % + 20 % = 70 %
remainder is 100 % - 70 % = 30 %
therefore 30 % of the cakes were sponge cakes