## Calculus (3rd Edition)

(a) $t=\frac{\ln10}{5}$ (b) $\frac{\ln 2}{5}$
(a) We have $$10=e^{5t}\\ 5t=\ln 10\\ t=\frac{\ln10}{5}$$ (b) The doubling time for $P$ is given by $\frac{\ln 2}{k}=\frac{\ln 2}{5}$.