50% of all the cakes Lucy bakes that week were party cakes: one fifth were fruit cakes and the remainder were sponge cakes. What percentage of cakes were sponge cakes ?
50% is equal to 5/10 so 5/10 were party cakes 1/5x2=2/10 so 2/10 were fruit cakes 5/10+2/10=7/10 so 10/10 which is 100% of all cakes 10/10-7/10=3/10 so 3/10 of the cakes were sponge cakes.
