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.

JOB ELEMENT OBSERVATIONS

(MINUTES) PERFORMANCE 1 2 3 4 5 6 7 RATING (%)

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

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?