50% of all cakes are party cakes. 1/5 were fruit. the rest were sponge, what is the percentage of sponge cakes?

If 1/5 of all the cakes are fruit, then 1-1/5=4/5 are sponge, which is 80/100, or 80%

if 1/5 of the party cakes are fruit, then 50% * 1/5=10% of the total cakes are fruit, so 100%-10%=90% are sponge