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Review practice:
Chapter 15
§ A work sampling study was performed during a three-hour final
exam to determine the proportion of time that students spend using
a calculator. There were 70 students taking the exam. A total of five
observations were taken of each student at random times during
the three hours. Of the total observations taken, 77 of the
observations found the students using their calculators.
§ (a) Form a 90% confidence interval on the proportion of time
students spend using their calculators during an exam.
§ (b) How many observations must be taken for the analyst to be
95% confident that the estimate of proportion of time a student
uses a calculator is within ±.03 of the true proportion?
2
§ The Chief IE in the production department wanted to know what value of PFD allowance to use for a
particular section of the shop. A work sampling study was authorized. Only three activity categories were
considered: (1) production work, (2) personal time, rest breaks, and delays, and (3) other activities. Over a
four - week period (40 hours/week), 100 observations were made at random times. Each observation
captured the category of activity of each of 22 production workers in the department. Results indicated that
category 2 constituted 19% of the total observations.
§ (a) Define the limits of a 95% confidence interval for activity 2.
§ (b) If a total of 522 work units were produced during the 4 weeks, and the 1540 observations in category 1
activity were all devoted to producing these units, what was the average time spent on each unit?
2
(b) Given Q = 522 work units

Chapter 13:
Seven cycles have been observed during a
direct time study. The mean for the largest
element time = 0.85 min, and the corresponding
sample standard deviation s = 0.15 min, which
was also the largest. If the analyst wants to be
95% confident that the mean of the sample was
within ± 10% of the true mean, how many more
observations should be taken?
=