Installing mufflers at the Stanley Garage in Golden, Colorado, involves five work elements. Linda Stanley has timed workers performing these tasks seven times, with the results shown in the following table.

By agreement with her workers, Stanley allows a 10% fatigue factor, a 10% personal-time factor but no time for delay. To compute standard time for the work operation, Stanley 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% confidencelevel?

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Observations (mintes) Performance Job Element 2 3 4 5 6 7 Rating (%) 1. Select correct 4 5 4 6 4 15a 4 6 87 6 7 6 7 15 14 14 12 15 I6 13 110 90 105 3 4 24a 5 4 3 18 100 130 mufflers 2. Remove old muffler 3. Weld/install new muffler 4. Check/inspect work 5. Complete paperwork 5 6 8 7 6 7 Employee has lenghy conversations with boss (not jcb related).