An investment is made at an annual rate of 9.71% compounded monthly, determine the number of months required for your investment to double.
After n interest periods, the amount is multiplied by
(1+r)^n
What you want is (1+r)^n = 2
(1+.0971/12)^n = 2
1.00809^n = 2
n ln 1.00809 = ln 2
n = ln 2/ln 1.00809
n = 86.02
So, after 86 months, the amount will be doubled.