We have to calculate the annual interest rate for the account. Formula for the simple interest is : I = P * r * t, where P is the investment, r is the annual interest rate and t is time in years. In this case: 1,800 = 10,000 * r * 4; 1,800 = 40,000 * r; r = 1,800 : 40,000; r = 0.045, or 4.5 %. Answer: The annual interest rate is 4.5 %
