Question 1103814
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The annual interest rate is 9%, or 0.09; the monthly interest rate is 0.09/12 = 0.0075.  The monthly growth factor is then 1+.0075 = 1.0075.<br>
We want to know how many months it takes for the overall growth factor to be 2, so that the original investment doubles.<br>
{{{(1.0075)^n = 2}}}
{{{n*log(1.0075) = log(2)}}}
{{{n = log(2)/log(1.0075) = 92.77}}}<br>
It will take 93 months for the investment to double in value; or, in years and months, 7 years and 9 months.