A discrete variable XXX has PMF P(X=k)=k10P(X=k) = \frac{k}{10}P(X=k)=10k for k∈{1,2,4}k \in \{1, 2, 4\}k∈{1,2,4}. What is E[X2]E[X^2]E[X2]?
8.5
10.5
7.5
9.5