Let X∼Gamma(α,β)X \sim \text{Gamma}(\alpha, \beta)X∼Gamma(α,β) (shape, scale). What is E[X]E[X]E[X]?
α/β\alpha / \betaα/β
αβ\alpha \betaαβ
α+β\alpha + \betaα+β
β/α\beta / \alphaβ/α