Chapter 4 - Discrete Random Variables - Exercises 4.50 - 4.76 - Learning the Mechanics - Page 205: 4.55e

$p(2)=0.3456$

$p=1-q=1-.6=.4$ $p(x)=\begin{pmatrix} n \\ x \end{pmatrix}p^xq^{n-x}$ $p(2)=\begin{pmatrix} 4 \\ 2 \end{pmatrix}(.4)^2(.6)^{4-2}=\frac{4!}{2!(4-2)!}(.16)(.6)^2=\frac{4(3)(2!)}{2!(2!)}(.16)(.36)=6(.16)(.36)=0.3456$