The Rule of 72

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Show your work for each problem.

1.
At 6% annual interest, approximately how many years will it take for an investment to double?
1. a)24 years
2. b)6 years
3. c)12 years
4. d)18 years
2.
Using the Rule of 72, how many years does it take for money to double at 9% interest?
3.
What interest rate is needed to double your money in 12 years?
1. a)6%
2. b)4%
3. c)8%
4. d)10%
4.
At 4% annual interest, how many years until your money doubles?
5.
Bank A offers 4% interest. Bank B offers 8% interest. How many years faster will your money double at Bank B?
6.
A credit card charges 18% interest. How many years until an unpaid balance doubles?
1. a)6 years
2. b)2 years
3. c)4 years
4. d)8 years
7.
If inflation is 3% per year, how many years until prices double?
8.
You invest 1000 dollars at 8% interest. How much will you have after 27 years?
9.
The Rule of 72 is most accurate for interest rates between:
1. a)1% and 3%
2. b)30% and 50%
3. c)4% and 12%
4. d)15% and 25%
10.
You want to double your money in 8 years. What interest rate do you need? (Enter just the number)
11.
You invest 2000 dollars at age 25 with 6% returns. How much will you have at age 61?
12.
If 1000 dollars becomes 4000 dollars in 18 years, what was the approximate interest rate?
1. a)12%
2. b)4%
3. c)8%
4. d)6%
13.
A 500 dollar credit card debt at 24% interest is never paid. How much is owed after 9 years?
14.
Using the Rule of 114, how many years to TRIPLE money at 6% interest?
15.
Why does the Rule of 72 use 72 instead of the mathematically exact number (69.3)?
1. a)69.3 is too small
2. b)72 is easier to divide mentally
3. c)Historical tradition only
4. d)72 gives more accurate results