Exercise 3 A production manager noticed that the mean time t

Exercise 3. A production manager noticed that the mean time to complete a job was 160 minutes. The manager made some changes in the production process in an attempt to reduce the mean time to finish the job. A stem-and-leaf plot of a sample of 11 times is as follows:

13 | 9

14 | 25

15 | 01356

16 | 24

17 | 0

Note: 14|5 = 145 minutes The sample mean and standard deviation are 153.36 and 9.47, respectively. Construct a 95% confidence interval for the mean time.

Solution

Sample size = 11

139, 142, 145, 150, 151, 153, 155, 156, 162, 164, 170

Mean = 153.364

std dev = 9.028

For 95% z value = 1.96

Margin of error = 1.96(9.028)/rt 11 = 5.34

Confidence interval = 148.03 to 158.7

= (148.03, 158.07)