Annual Intrest Rate

Question

What annual rate of interest compounded annually is required to double an investment in 13 years?

Answer 1

A= P(1+r)^t

A/P = 2=(1+r)^13

solve for r

1+r = 13th root of 2

r = 13th root of 2 minus 1

= (2^(1/13)) - 1

r=about 0.0548 = 5.48%