A time analyst for the Super-Fast speedway pit crew observed the mechanic in charge of changing both front tires during a pit-stop practice session. The mechanic’s job is divided into six work elements and a preparation time between drills. The element times (in seconds) for the first six cycles are shown in Table H.5.
a. Calculate the normal time for changing tires.
b. What sample size is appropriate for estimating the average time for work element 3 within ±1 percent of the true mean with 99 percent confidence?
c. What is the standard time for changing tires if the allowance is 20 percent?

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TABLE H.5 PIT CREW TIME STUDY DATA OBSERVATION Work Element 4 RF 1. Wait for car lift 0.5 2.9 3.2 2.6 1.0 2. Remove lugs 3.3 3.8 3.6 3.8 4.0 4.3 1.0 0.9 3. Switch tires 6.4 6.2 6.4 7.1 6.8 7.3 1.0 1.2 4. Tighten lugs 3.5 4.1 3.8 3.5 4.9 4.2 1.0 0.8 5. Move to right side 3.2 3.8 4.3 0.5 1.2 6. Clear away for drop 0.5 2.7 2.1 2.0 0.9