Sally’s parents deposited $15,000 into a college savings account on her third birthday. The account had an interest rate of 9.6% compounded annually. They were hoping that the money would double twice by the time she was 18 years old. Using the rule of 72, mc009-1.jpg will their hopes come true? Yes, the $15,000 will double each 7.5 years. In 15 years, it will double twice. Yes, the $15,000 will double in 7.5 years and be four times as much in 15 years. No, the $15,000 will only double once in 15 years, not double twice. No, it will take 30 years for the $15,000 to double twice.