17. Noise and Stress To compare the effect of stress caused by noise on the ability to perform a simple task, 70 subjects were divided into two groups—30 subjects as a control group, and 40 subjects as the experimental group. Although each subject performed the task, the experimental group had to perform the task while loud rock music was played. The time to finish the task was recorded for each subject and the following summary was obtained:

a. Find a 99% confidence interval for the difference in mean completion times for these two groups.

b. Based on the confidence interval in part

a, is there sufficient evidence to indicate a difference in the average time to completion for the two groups? Explain.

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SKS n Control 30 Experimental 40 15 minutes 23 minutes 4 minutes 10 minutes