Question

A random variable X has the following probability distribution:X	-2	-1	0	1	2
P(X)	0.2	0.1	0.3	0.2	0.2

The variance of X will be:

• A. 0.1
• B. 1.42
• C. 1.89
• D. 2.54

Answer 1

Answer: (C)

1.89

Answer 2

Variance is calculated as:

$\text{Var}(X) = E(X^2) - [E(X)]^2.$

First, calculate $E(X)$:

$E(X) = \sum X \cdot P(X) = (-2)(0.2) + (-1)(0.1) + (0)(0.3) + (1)(0.2) + (2)(0.2).$

$E(X) = -0.4 - 0.1 + 0 + 0.2 + 0.4 = 0.1.$

Next, calculate $E(X^2)$:

$E(X^2) = \sum X^2 \cdot P(X) = (-2)^2(0.2) + (-1)^2(0.1) + (0)^2(0.3) + (1)^2(0.2) + (2)^2(0.2).$

$E(X^2) = 4(0.2) + 1(0.1) + 0(0.3) + 1(0.2) + 4(0.2) = 0.8 + 0.1 + 0 + 0.2 + 0.8 = 1.9.$

Finally, calculate the variance:

$\text{Var}(X) = E(X^2) - [E(X)]^2 = 1.9 - (0.1)^2 = 1.9 - 0.01 = 1.89.$