The Rule of 72estimates how long it takes for a given amount of money to double in value ata fixed compound interest rate. For example,investing $1,000in a high-yield savings account will earn about1%interest per year.So,in a few decades (7.2)your money will double.Of course, at 1%per month,the doubling would be in 72months.

(Notice the doubling period is always in the same units of time as the interest rate.Usually,interest is described in annual rates;therefore,the doubling time is in years.)

Assume you want toretire at age 60.How much money do you think you will need?What interest rate do you think is a reasonable expectation?By what age will you need to have saved 50% of the final amount?How can you change the time?Explain.