Chapter 4, Exponential and Logarithmic Functions - Section 4.5 - Exponential and Logarithmic Functions - 4.5 Exercises - Page 405: 97

(a). $P=7.337$ (b). $t=1.733$

$P=\frac{10}{1+4e^{-0.8t}}$ (a). for $t=3,$ $P=\frac{10}{1+4e^{-2.4}},$ $P=7.337$ (b). $5=\frac{10}{1+4e^{-0.8t}},$ $5(1+4e^{-0.8t})=10,$ $1+4e^{-0.8t}=2,$ $e^{-0.8t}=0.25,$ $-0.8t=\ln {0.25}$ $t=1.733$