Joey put $11.64 in his piggy bank. If he doesn’t touch his money for 3 months, his parents will give him 10% interest on his money. How much interest will Joey earn on savings if he doesn’t touch it for 3 months and how much will he have in total after his parents pay him the interest?

There are two basic forms of interest - simple interest and compound interest.  

For simple interest the formula is:

I = PRT (interest equals principal, interest rate and time)

The principal is the actual amount of money you borrow or put into a savings account.