20. Noise and Stress In Exercise 17 (Section 8.4), you compared the effect of stress in the form of noise on the ability to perform a simple task. A group of 30 subjects acted as a control, while a group of 40 (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. Is there sufficient evidence to indicate that the average time to complete the task was longer for the experimental “rock music” group? Test at the 1%
level of significance.

b. Construct a 99% one-sided upper bound for the difference (control – experimental) in average times for the two groups. Does this interval confirm your conclusions in part a?

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n X S Control 30 15 minutes 4 minutes Experimental 40 23 minutes 10 minutes