Question

For a random variable X, if Var (X) = 5 and E (X²) = 21, the value of E (X) is ______

Options

• 3

• 4

• 5

• 6

Answer 1

For a random variable X, if Var (X) = 5 and E (X²) = 21, the value of E (X) is 4.

Explanation:

Since Var (X) = E(X²) - [E(X)]²

∴ 5 - 21 - [E(X)]²

∴ [E(X)]² = 21 - 5 = 16

∴ E(X) = 4