Five friends all brought some cakes with them when they met. Each of them gave a cake to each of the others. They then ate all the cakes they had just been given. As a result, the total number of cakes they had between them decreased by half. How many cakes did the five friends have at the start?

Abank manager wants to encourage new customers to open accounts with principals of at least $2,500. he decides to make a poster advertising a simple interest rate of 3%. what must the principal be if the bank manager also wants to advertise that one can earn $10 the first month? can the poster correctly say, "open an account of $2 comma 500 and earn at least $10 interest in 1 month! "?