Rule of 72 Earlier, we discussed the Rule of 72, a useful approximation for many interest rates

Question:

Rule of 72 ‘Earlier, we discussed the Rule of 72, a useful approximation for many interest rates and periods for the time it takes a lump sum to double in value. For a 10 percent interest rate, show that the “Rule of 73” is slightly better. For what rate is the Rule of 72 exact? (Hint: Use the Solver function in Excel.)