How long it will take to double an investment if rate of return is 10% compounded monthly?

Question

 How long it will take to double an investment if rate of return is 10% compounded monthly?

Answer 1

A = P(1 +r/n)^nt r=.10, n=12 months t= years

2 = (1+.10/12)^12t

2 = 1.008333^12t

12t= 83.47

t = 83.47/12 = about 6.9 years to double the investment

A= Pert for continuously compounded interest

2 =e.1t

ln2 =.1t

t = ln2/.1 = 10ln2 = about 6.9 years to double the investment