Question

Becky invests some money that she anticipates will average an annual return of 7%. About how many years will it take Becky’s money to double at this rate? Show your work using function notation.

Answer 1

The number of years it would take Becky to double the amount invested is 10 years.

The rule of 70 is a rule of thumb that is used to know the number of years it would take an investment to double at the interest rate. The formula entails dividing 70 by the interest rate.

Rule of 70 = 70 / interest rate

70 / 7 = 10 years

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Answer 2

Answer:

• About  14.3 years

Step-by-step explanation:

The function for this case would be:

• f(x) = 7x, where f(x) is the average return of %, x - is the number of years

If we need the money to double, the return rate should be 100%:

• 7x = 100
• x = 100/7
• x = 14.3 years