7.37 Is the difference important?
Give a 90% confidence interval for the mean time advantage of right-hand over left-hand threads in the setting of the previous exercise. Do you think that the time saved would be of practical importance if the task were performed many times—for example, by an assembly-line worker? To help answer this question, find the mean time for right-hand threads as a percent of the mean time for left-hand threads.
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7.37
The 90% C.I. is . The mean time for right-hand threads is 104.12, for left it is 117.44. The ratio is 88.66%. On an assembly line with an 8-hour period, this amounts to saving more than 54 minutes or almost an entire hour of time. This seems like a substantial practical gain.