Answer:
9.9 years
Step-by-step explanation:
There are two ways to go at this. For this problem, they give the same answer.
<u>Quick way</u>:
The interest rate is 7.25%. Using the "rule of 72" the doubling time in years is ...
doubling time in years = 72/(interest rate %)
72/7.25 ≈ 9.9 . . . years
__
<u>Exact Calculation</u>:
The initial investment is 750, so it will be double when A(t) = 1500. Filling in the value and solving for t, you have ...
1500 = 750(1.0725^t)
2 = 1.0725^t . . . . . . divide by 750
log(2) = t·log(1.0725) . . . . . take logarithms
Divide by the coefficient of t
t = log(2)/log(1.0725) ≈ 9.9 . . . . years
