Question

From a study conducted of 250 online shoppers, an online retailer determined that the average amount of time shoppers who shop online at night is 20 minutes. The population standard deviation is assumed to be 3 minutes. Estimate the population mean time spent shopping online at the 90% confidence level. (5 points)

Interpretation: We are ________ confident that the that the population mean time spent shopping online at night is between ________ minutes and ________ minutes.

Answer 1

Sample size = n = 250

Sample mean = = 20

Population standard deviation = = 3

We have to construct 90% confidenc interval for the population mean.

Here population standard deviation is known so we have to use one sample z-confidence interval.

z confidence interval

Here E is a margin of error

Zc = 1.64 ( Using z table)

So confidence interval is ( 20 - 0.3112 , 20 + 0.31112) = > ( 19.6888 , 20.3112)

Interpretation: We are 90% confident that the that the population mean time spent shopping online at night is between 19.6888 minutes and 20.3113 minutes.