
Chapter 8
PB
Sampling and Sampling Distributions
293
Example 8.3
In a grocery store, the mean expenditure per customer is `2000 with a standard deviation of `300.
If a random sample of 50 customers is selected, what is the probability that the sample average
expenditure per customer is more than `2080?
Solution: As discussed in the chapter, the z formula is given as below:
z
x
n
=
σ
Here, Population mean (
μ
) = 2,000
Population standard deviation (
σ
) = 300
Sample size (n) = 50
Sample mean
= 2080
By substituting all these values in the z
formula, we get the z score as below:
z =
2080 2000
300
50
80
42 4268
188
.
.
z = 1.88
So, the required area under normal ...