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 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 following summary was obtained:

Control Experimental

n 30 40

x bar 15 minutes 23 minutes

s 14 minutes 10 minutes

Is there sufficient evidence to indicate that the average time to complete the task was longer for the experimental rock music group ? Test at 1% level of significance

Construct a 99% confidence interval for the difference (control-experimental) in average times for the two groups. Does this interval confirm your conclusions in part a ?