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})
