Solutions - 5080-04

(a)

$$\begin{array}{c}P[\text{pass}]=\sum _{k=3}^4\left(\genfrac{}{}{0px}{}{4}{k}\right){(0.8)}^k{(0.2)}^{4-k}\\ \\ \gg \gg \approx 0.8192\end{array}$$

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(b)

Out of the remaining three questions, you need to answer at least two correctly.

$$\begin{array}{c}P[\text{pass}]=\sum _{k=2}^3\left(\genfrac{}{}{0px}{}{3}{k}\right){(0.8)}^k{(0.2)}^{3-k}\\ \\ \gg \gg \approx 0.896\end{array}$$