## Precalculus (6th Edition) Blitzer

$a.\quad 25.1$ million $b.\quad$ in $2015$
$a.$ In the year 2010, t is 0. Substitute 0 for t in the formula and calculate. $A=25.1e^{0}$ = $25.1$ million. $b.$ Solve for t when $A=28.$ $28=25.1 e^{0.0187t}\quad$ ... $/\div 25.1$ $\displaystyle \frac{28}{25.1}=e^{0.0187t}\quad$ ... $/\ln(...)$ $\displaystyle \ln(\frac{28}{25.1})=0.0187t \quad$ ... $/\div 0.0187$ $t=\displaystyle \frac{\ln(\frac{28}{25.1})}{0.0187}\approx 5.847$ (years after 2010) The population will reach $28$ million in $2015$.