Answer: 12%
Explanation: Rule of 72 says that to know in how many years the amount can double can be done by using the interest rate. The rule of 72 says that 72 divided by the annual interest rate will give the number of years it will take to double the amount.
Rule of 72:
72 ÷ rate of interest = Number of years
Rate of interest = ?
Number of years to double the investment = 72 ÷ r
6 = 72 ÷ r
r = 72 ÷ 6
r = 12%
Therefore, in order to get $2 for every $1 invested, the rate of interest would be 12%
