how many years will it take to double in value?

Question

Use the amortization function 

If an investment has a 5% annual interest rate and it is compounded monthly, how many years will it take to double in value? Round your answer to the nearest tenth.

Answer 1

Let p = principal then 2p =p*(1+(.05/12))^m where m = months

2 = (1.00417)^m log 2 = m*log(1.00417)

So, m = 166.7 months or 13.89 years