The rule of 70 applies in any growth-rate application. Let’s say you have $2000.00 in savings and you have three alternatives for investing these funds.
A savings account earning 1% interest per year. A U. S. Treasury bond mutual fund earning 3% interest per year. A stock market mutual fund earning 8% interest per year.

How many years would it take to double your savings in each of the following three accounts? In all cases, give your answers to two decimals.

(a)70 years

(b)23.33 years

(c)8.75 years

Explanation:

According to the Rule of 70, for a given interest rate x, funds double in years.

(a)For a savings account earning 1% interest per year,

The number of years it will take the fund to double= =70 years

(b)For a U.S. Treasury bond mutual fund earning 3% interest per year.

The number of years it will take the fund to double= =23.33 years

(c)For a stock market mutual fund earning 8% interest per year.

The number of years it will take the fund to double= =8.75 years

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