If four friends can eat four cakes in four days, then how many cakes can 10 friends eat in 10 days?

25 cakes per 10 days

If four friends can eat four cakes in four days, then four friends will eat an average of one cake per day, so each friend will be able to eat 1/4 of a cake per day. So 10 friends will eat 10/4 of cake per day, or two and a half cakes per day, so they will eat 2,5 * 10 = 25 (twenty-five) cakes per 10 days, assuming they will eat at the same rate