Consumer Math 4.2 Rule of 72 and 69

Your returns (or interest rate) are 8% a year. How long before your investment doubles?

• 9 years
• 8 years
• 7 years
• Never

Your returns (or interest rate) are 9% a year. How long before your investment doubles?

• 9 years
• 8 years
• 7 years
• They won't

Your returns (or interest rate) are 6% a year. How long before your investment doubles?

• 18 years
• 16 years
• 12 years
• 8 years

Your returns (or interest rate) are 1% a year because they are in a savings account. How long before your savings doubles?

• 72 years
• 36 years
• 1 year
• They will never double

How many years will it take $4000 to double with a 5% interest rate?

• 1440
• 14.4
• 55.5
• 80

What interest rate would you need to double $3500 in 9 years?

• 7%
• 10%
• 8%
• 38.8%

How many years will it take $600 to double with 10% interest?

• 6 years
• 8.3 years
• 10 years
• 7.2 years

What interest rate would you need to double $2500 in 12 years?

• 5%
• 6%
• 34%
• 16%

How many years will it take to double your money with a 3% interest rate?

• 24 years
• 12 years
• 4 years
• none of these

What calculation should you do to answer the question:

How many years will it take $900 to double if the interest rate is 2%?

• 72 divided by 2

• 900 divided by 2

• 2 divided by 100 times 900