Final answer:
The scenario with the smallest doubling time is the one with the highest interest rate compounded more frequently. The scenario with 3.1% annual interest, compounded monthly, has the smallest doubling time of approximately 22.58 years.
Step-by-step explanation:
The scenario with the smallest doubling time is the one with the highest interest rate compounded more frequently. In this case, the scenario with 3.1% annual interest, compounded monthly, has the smallest doubling time. To determine the doubling time, we can use the rule of 70, which states that the doubling time is approximately 70 divided by the interest rate. Therefore, the doubling time for the scenario with 3.1% annual interest, compounded monthly, would be approximately 22.58 years.