Khan.randRange(1,9) Khan.randRange(2*N,4*N)

An investor places $N,000 into a stock fund. 10 years later the account has a value of $M,000. Using logarithms and antilogarithms, determine the average annual growth rate for this fund. (Round to the nearest integer.)

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answer = parseFloat(guess[0]); return checkAnswer(answer, M , N);

If you start with N and in 10 years you get M, then you want to solve for X in the equation N * X^{10} = M.

You will need to use logs/antilogs. Fortunately, you can use whatever base you want for the logarithm. Since many scientific calculators will calculate the natural log (base e, called \ln) and will also give you e^x, this might be the easiest base to work with.

Solving for X gives us:
X^{10} = M/N
10 \ln X = \ln M/N
\ln X = (\ln M/N)/10
X = e^{(\ln M/N)/10}
Find a calculator that can solve this for you.

If X is a number like 1.123, then the annual percentage increase is 12.3%, which to the nearest integer is 12%.