[Math] Find the time required for an investment to grow to a given amount with compound interest

calculusexponential function

Find the time required for an investment of 5000 dollars to grow to 7400 dollars at an interest rate of 7.5 percent per year, compounded quarterly.
Your answer is t= years.

I got to the point where i have $74000=5093.55^{4t}$ and then I tried putting natural logs in front of both sides of the equation but from there I can't seem to cancel out what I want to to solve for t.

Best Answer

Solve $$A=P\left( 1+\frac{r}{n} \right)^{(nt)}$$ for $t$ with your values included in the formula.

Recall from properties of logarithms: $$ \begin{align*} y=x^k \Rightarrow \log y &= \log x^k \\ &=k\log x. \end{align*} $$ Hence $$k=\frac{\log y}{\log x}.$$

It looks like that exponent rule is where you are getting hung up.