Installing mufflers at the O'Sullivan Garage in Golden, Colorado, involves five work elements. Jill O'Sullivan has timed workers performing these tasks seven times, with the results shown in the following table:
By agreement with her workers, Jill allows a 10% fatigue factor and a 10% personal-time factor, but no time for delay. To compute standard time for the work operation, Jill excludes all observations that appear to be unusual or nonrecurring. She does not want an error of more than {5%.
a) What is the standard time for the task?
b) How many observations are needed to assure a 95% confidence level?