Final answer:
It would take at least 4 complete years for a sum of money to more than double with a compound interest rate of 20% per year, based on the Rule of 72.
Step-by-step explanation:
The question is seeking to determine the least number of complete years required for a sum of money to more than double when compounded annually at a 20% interest rate. To find the number of years needed to double the initial investment, we can use the Rule of 72, a simple formula in finance that estimates the time required to double an investment at a fixed annual rate of return.
The Rule of 72 states that you divide 72 by the annual interest rate to get an approximation of how many years it will take for the initial investment to double. In this scenario, dividing 72 by the annual rate of 20% gives us 3.6 years. Since only whole years count, we need to round up to the nearest whole number, which means it would take at least 4 years for the sum of money to more than double with compound interest at an annual rate of 20%.