Answer:
30% sponge cakes.
Step-by-step explanation:
We have been given that 50% of all the cakes jenny baked that week were party cakes, 1/5 were fruits cake.
Let us convert 1/5 into percentage as:



Therefore, 20% of cakes are fruit cake.
Now, we will find remainder by subtracting 20 plus 50 percent from 100 percent as:



Therefore, the percentage of the sponge cakes is 30%.