Question

If you deposit money today in an account that pays 6 percent annual interest, how long will it take to double your money?

Answer 1

Lets say you deposit 40000 dollars.
You have to determine how much time it will take for your money to become
80000 dollars.
Future Value = Present Value*((1+r)^t)
where r is the interest rate that is 6% and t is the time period in years.
80000 = 40000*((1.06)^t)
2 = (1.06)^t
take natural log on both sides
tln(1.06) = ln(2)
t = ln(2)/ln(1.06)
t = .693147/.058269
t = 11.896 years.
It will take 11.896 years.