Solutions - 5110-09

$X\sim \mathrm{Pascal}(2,0.1)$

$$\begin{array}{c}P[X\ge 4]=1-(P[X=2]+P[X=3])\\ \\ \gg \gg 1-({(0.1)}^2+\left(\genfrac{}{}{0px}{}{2}{1}\right){(0.1)}^2{(0.9)}^1)\gg \gg 0.972\end{array}$$