SCENARIO 18-4
a Factory Supervisor Is Concerned That the Time

question 119

Multiple Choice

SCENARIO 18-4
A factory supervisor is concerned that the time it takes workers to complete an important production
task (measured in seconds) is too erratic and adversely affects expected profits. The supervisor
proceeds by randomly sampling 5 individuals per hour for a period of 10 hours. The sample mean and
range for each hour are listed below. $$\begin{array} {ccc} \underline {\text { Hour }} & \underline { \bar { X } } & \underline { R } \\1 & 18.4 & 25 \\2 & 16.9 & 27 \\3 & 23.0 & 30 \\4 & 21.2 & 23 \\5 & 21.0 & 24 \\6 & 24.0 & 25 \\7 & 19.3 & 12 \\8 & 15.8 & 14 \\9 & 20.0 & 13 \\10 & 23.0 & 11\end{array}$$ She also decides that lower and upper specification limit for the critical-to-quality variable should be
10 and 30 seconds, respectively.
-Referring to Scenario 18-4, suppose the supervisor constructs an $\bar { X }$ chart to see if the process is in-control. What are the lower and upper control limits of this chart?

• A) 10.00, 30.00
• B) 8.49, 32.03
• C) 5.39, 35.13
• D) 4.96, 35.56

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Definitions:

Null Hypothesis

A statistical hypothesis that indicates no effect or no difference in the context of scientific experiments, assuming the observation results from chance.

Control

The use of standardized procedures and conditions in scientific experiments to ensure that changes observed in an experiment are due to the manipulation of the independent variable.