Answer
$ 11.612\%$
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 $A=3P$, after $t=10$ years, with $n=1$ compounding period per year.
$3P =P\displaystyle \left(1+\frac{r}{1}\right)^{10(1)} \quad/\div P$
$3=(1+r)^{10} \quad/ \sqrt[10]{...}$
$\sqrt[10]{3}=1+r\quad/-1$
$r=\sqrt[10]{3}-1\approx 0.11612$
$ r\approx 11.612\%$
