math (interests & percentss)
posted by bree .
i need help with these problems below !
mike deposited $500 for 9 months at 8%, compounded quarterly.
a. how many times was interest added to mike's account?
b. what percent interest was added each time?
c. what was the balance in mike's account at the end of 9 months?
sara deposited $1400 for 1 year at 10%, compounded semiannually.
a. how many times was interest added to sara's account?
b. what percent interest was added each time?
c. what was the balance in sara's account at the end of one year?
i don't understand how to do these problems so please explain & show work.

$21.60