Answer
at about age 48.
Work Step by Step
We solve for x when P(x)=$50\%=0.5$
$0.5=\displaystyle \frac{0.9}{1+271e^{-0.122t}}\qquad.../\times 2(1+271e^{-0.122t})$
$1+271e^{-0122\mathrm{r}}=1.8$
$271 \mathrm{e}^{-0.122t} =0.8\qquad.../\div 271$
$e^{-0.122t}=\displaystyle \frac{0.8}{271}\qquad .../$apply ln( ) to both sides
$-0.122t=\displaystyle \ln\frac{0.8}{271}$
$ t=\displaystyle \frac{\ln\frac{0.8}{271}}{-0.122}\approx$47.7480522311
The probability of some coronary heart disease is 50\% at about age 48.
