Question

A marketing research company desires to know the mean consumption of milk per week among males over age 22. A sample of 715 males over age 22 was drawn and the mean milk consumption was 4.2 liters. Assume that the population standard deviation is known to be 1.3 liters. Construct the 90% confidence interval for the mean consumption of milk among males over age 22. Round your answers to one decimal place.

Answer 1

We want to find 90% confidence interval for mean consumption of milk per week μ
The formula of confidence interval is as follow:

Lower limit =
Upper limit =
Where E is the margin of error
the formula of margin of error is as follows:

given information is -

For confidence level =0.90

(I have used standard normal distribution table)
Therefore,

Lower limit == 4.2 - 0.10 =4.1
Upper limit = =4.2 + 0.10 =4.3

Thus, 90% confidence interval for mean consumption of milk per week μ  is (4.1 , 4.3 )

Interpretation: We are 90% confident that this interval will include the true value of μ.