Question

Chris invests $12,000 in an account. The interest is compounded monthly at an annual rate of 11.6%. The ending account balance will be $33,916.21. How many years was the investment accruing interest?

--use a TVM calculator

Answer 1

i = .116/12 = .0096666...
n = ? , where n is in months.

12000(1.009666..)^n = 33916.21
(1.009666...)^n = 2.82635...

take log of both sides, applying standard log rules:
n log 1.0096666... = lof 2.82635..
n = 108 correct to 5 decimal places

108 months = 9 years