SOLUTION
To solve this we will use the form for exponential growth to determine the formula to use.
Exponential growth has the form
[tex]\begin{gathered} P=P_0e^{rt} \\ P=\text{population after timer t} \\ P_0=\text{ initial population growth } \\ r=\text{ percent growth rate} \end{gathered}[/tex]
Now the frogs tripple in population after 9 days. Initially they were 21. So in 9 days they become
[tex]21\times3=63\text{ frogs }[/tex]
Applying the formula, we have
[tex]\begin{gathered} P=P_0e^{rt} \\ 63=21e^{9r} \\ 3=e^{9r} \\ \text{taking ln of both sides } \\ \ln 3=\ln e^{9r} \\ \ln 3=9r \\ r=\frac{\ln3}{9} \end{gathered}[/tex]
The time for the frogs to get to 290 becomes
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