8.1 A Confidence Interval When the Population Standard Deviation Is Known or Large Sample Size
Building a z-based interval around a sample mean, choosing critical values from the confidence level, and reading the margin of error.
3 exercises
8.1 Exercise 2
Suppose average pizza delivery times are normally distributed with an unknown population mean and a population standard deviation of six minutes. A random sample of 28 pizza delivery restaurants is taken and has a sample mean delivery time of 36 minutes.
Find a 90% confidence interval estimate for the population mean delivery time.
8.1 Exercise 5
Suppose we change the original problem in the example to see what happens to the confidence interval if the sample size is changed.
Leave everything the same except the sample size. Use the original 90% confidence level. What happens to the confidence interval if we increase the sample size and use n = 100 instead of n = 36? What happens if we decrease the sample size to n = 25 instead of n = 36…
8.1 Exercise 8
The price of a chair is a large range of cost. The average cost of 25 chairs in a store is $100. The sample standard deviation is $50. Construct a 92% confidence interval for the population mean of the cost of chairs.
Adapted from Introductory Business Statistics 2e © 2023 Rice University. Licensed under CC BY 4.0. Source: Introductory Business Statistics 2e. Imported at revision 50ec917.