What is the expected value of a random variable X where P(X=10)=0.3 and P(X=20)=0.7?

What is the expected value of a random variable X where P(X=10)=0.3 and P(X=20)=0.7?

Approach: Sum of values weighted by probabilities.

17. (10 * 0.3) + (20 * 0.7) = 3 + 14 = 17.

Follow-up: What is the variance?

Key concepts: mean.