Question

The time it takes to double the balance in an account varies inversely with interest rate. If you invest $1,000 at 6% it will take 12 years to double your money. Find the time it will take to double your money at 4 %

Answer 1

18 years

Explanation:

At 2/3 the interest rate, the doubling time goes up by a factor of 1/(2/3) = 3/2.

(3/2)(12 years) = 18 years