confirm question 9 Please see below I got two conflicting a

confirm question 9 // Please see below I got two conflicting answers who is right??

A production manager is trying to determine the amount of time needed to complete a particular task. She takes a random sample of 20 workers and asks each one to keep track of his/her time. Their records in minutes are given below. Assume that the distribution of times to complete this certain task is approximately normal. A) Find the point estimate for mu, the mean amount of time needed to complete the task B) Construct a 95% confidence interval for the population mean amount of time to complete the task. Show your work or calculator command. C) Interpret this interval in the context of the problem. Use complete sentences. D) What is the margin of error? E) Another manager claims that during the holiday season, the workers can take a mean amount of 135 minutes to finish the task. Does this contradict your findings above? Justify your answer and be specific.

Solution

The second one is correct. The problem with the first one is that you didn\'t divide the sample standard deviation by sqrt 20 (necessary to get standard error) and you used a Z distribution rather than a T distribution. The T distribution is necessary because we don\'t know the population standard deviation and we have to estimate it from the sample.