7.2 Mean and Variance of Discrete Random Variables
Formulas
Mean = μ = Σ x i p i
Variance = σ2 = Σ(x i - μ)
Standard Deviation = 2
pi
σ = √ Σ(x i - μ)
2
pi )
Example 1
Find the mean and the standard deviation of the following information.
Cars Sold
Probability
xi
0
0.3
pi
1
0.4
x i ­ μ
2
0.2
( x i ­ μ) 2
3
0.1
( x i ­ μ) 2 p i