单选题 Given P(X=2) =0.3, P(X=3) =0.4, P(X=4) =0.3. What is the variance of X?

A、

A.0.3.
B、

B.0.6.
C、

C. 3.0.

【正确答案】 B

【答案解析】
The variance is the sum of the squared deviations from the expected value weighted by the probability of each outcome.
The expected value is E(X) =0.3×2+0.4×3+0.3×4=3.
The variance is 0.3×(2-3)²+0.4×(3-3)2 +0.3×(4-3)²=0.6.