Question

Determine the mean and variance of the random variable with the following probability mass function. f(x)=(216/43)(1/6)x, x=1,2,3 Round your answers to three decimal places (e.g. 98.765).

Answer 1

Mean:

E[X] = ∑ x f(x) = 1 × f (1) + 2 × f (2) + 3 × f (3) = 51/43 ≈ 1.186

Variance:

Recall that for a random variable X, its variance is defined as

Var[X] = E[(X - E[X])²] = E[X ²] - E[X]²

Now,

E[X ²] = ∑ x ² f(x) = 1² × f (1) + 2² × f (2) + 3² × f (3) = 69/43

Then

Var[X] = 69/43 - (51/43)² = 366/1849 ≈ 0.198

(each sum is taken over x in the set {1, 2, 3})