Answer
$ 25.992\%$
Work Step by Step
The amount A after t years due to a principal P
invested at an annual interest rate r, expressed as a decimal,
compounded n times per year is $A=P\displaystyle \cdot\left(1+\frac{r}{n}\right)^{nt}$
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We want A=2P, after t=3 years, with n=1 compounding period per year.
$2P =P\displaystyle \left(1+\frac{r}{1}\right)^{3(1)} \quad/\div P$
$2=(1+r)^{3} \quad/ \sqrt[3]{...}$
$\sqrt[3]{2}=1+r\quad/-1$
$r=\sqrt[3]{2}-1\approx 0.25992$
$ r\approx 25.992\%$
