The process of replacing an old tire for customers at Tire Tech.company involves five work elements. The table below shows the results of a time study of the process performed by the manager on seven occasions.

a) What is the standard time for the process if the company use an allowance factor of 8%?
b) How many observations are needed to assure 95% confidence level?

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OBSERVATIONS (MINUTES) 1 2 3 4 5 6 7 15 18 25 22 16 18 19 2.8 3.2 2.4 1.7 2.7 2.9 2.5 1.2 1.1 1.4 1.3 1.3 1.4 1.1 2.1 2.2 1.9 1.6 2.0 2.4 2.2 3 4 JOB ELEMENT 1. Decide on a brand 2. Lift car and remove nuts 3. Remove old tire 4. Install new tire 5. Issue invoice and payment 4 5 5 5.0 PERFORMANCE RATING (%) 90 90 85 100 110