If 1/5 of the cakes are fruitcakes, then [tex]1- \frac{1}{5} = \frac{4}{5} [/tex] of the cakes are sponge cakes. To convert to a percentage, we simply multiply by 100, for a result of [tex] \frac{4}{5}*100= \frac{400}{5}=80 [/tex] percent sponge cakes.
