Chapter 3 - Section 3-4 - Mean and Variance of a Discrete Random Variable - Exercises - Page 77: 3-70

$E(x)=271.18, V(x)=10.1076$

$\begin{aligned} \mathbb{E}(X) &=266 \times 0.24+271 \times 0.3+274 \times 0.46=271.18 \\ \mathbb{E}\left(X^{2}\right) &=266^{2} \times 0.24+271^{2} \times 0.3+274^{2} \times 0.46=73548.7 \\ \operatorname{Var}(X) &=\mathbb{E}\left(X^{2}\right)-\mathbb{E}(X)^{2}=10.1076\end{aligned}$