32 THE BASICS OF INTEREST THEORY Practice Problems Problem 4.1 You invest $100 at time 0, at an annual simple interest rate of 9%. (a) Find the accumulated value at the end of the fifth year. (b) How much interest do you earn in the fifth year? Problem 4.2 At what annual rate of simple interest will $500 accumulate to $615 in 2 years? Problem 4.3 In how many years will $500 accumulate to $630 at 7.8% annual simple interest? Problem 4.4 What principal will earn interest of 100 in 7 years at a simple interest rate of 6%? Problem 4.5 What simple interest rate is necessary for $10,000 to earn $100 interest in 15 months? Problem 4.6 At a certain rate of simple interest $1,000 will accumulate to $1110 after a certain period of time. Find the accumulated value of $500 at a rate of simple interest three fourths as great over twice as long a period of time