How long will it take money to quadruple if it is invested at the following​ rates? ​(A) 3.3​% compounded semiannually? ​(B) 15​% compounded semiannually?

Answer 1

This question requires us to use the compound interest formula, which is A = P(1 + r/n)^(nt). In the formula, r is the annual rate, and n is the number of compounding periods during one year. From your problem, we can plug in what we already know like this: A = P(1 + .033/2)^(2t). From there, we know that we want to quadruple our investment, so we can replace A and P to indicate that: 4 = 1(1 + .033/2)^(2t). When we simplify this equation, we get 4 = 1.0165^(2t). Solving for t gives us 42.3545 years. If we use 15% instead, we get 9.58 years.