9.29 Noise and Stress In Exercise 8.55, you compared the effect of stress in the form of noise on the ability to perform a simple task. Seventy subjects were divided into two groups; the first group of 30 subjects acted as a control, while the second group of 40 was the experimental group. Although each subject performed the task in the same control room, each of the experimental group subjects had to perform the task while loud rock music was played. The time to finish the task was recorded for each subject and the follow- ing summary was obtained: 

a. Is there sufficient evidence to indicate that the aver- age 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 975 Control 30 15 minutes 4 minutes Experimental 40 23 minutes 10 minutes