a group of researchers is conducting a study to determine the average time to fix a rivet at a particular location on an assembly line. at a 95% confidence level, they do not want the average time of their sample to be off by more than 3.5 seconds (could also be stated as: the width of the total deviation from the mean time to be at most 7 seconds). from previous studies, the variance is known to be 55 seconds2. what sample size should be used in this study?
