For a discrete random variable $X$ taking values $x_i$ with probabilities $p_i$, the mean $E(X)$ is given by
A$\sum x_i^2 p_i$
B$\sum x_i p_i$
C$\left(\sum x_i p_i\right)^2$
D$\sum p_i^2$
Answer & Solution
Correct answer: B. $\sum x_i p_i$
The expectation or mean of a discrete random variable is the weighted average of its values, with weights equal to their probabilities: $E(X)=\sum x_i p_i$.
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