31) A study of 200 insomniacs paid for by the Serta Mattress Company found that

Question

31) A study of 200 insomniacs paid for by the Serta Mattress Company found that the average insomniac counted 350 sheep before falling asleep, with a standard deviation of 120. An insomniac is a person who has difficulty falling asleep. Some useful numbers might be:



=NORMSINV(0.89) 1.2265
=NORMSINV(0.945) 1.5982
=TINV(0.89,199) 0.1385
=TINV(0.11,199) 1.6053
=TINV(0.055,199) 1.9302



Calculate an 89% confidence interval for the true mean number of sheep counted by insomniacs.

A. 350±13.56
B. 350±10.41
C. 350±16.38
D. 350±13.62



32) What does it mean to have 95% confidence in an interval estimate?

A. In repeated sampling, 95% of the intervals would contain the population parameter.
B. In repeated sampling, the population parameter would fall in the given interval 95% of the time.
C. In repeated sampling, 95% of the point estimates fall within the given interval.
D. In repeated sampling, 95% of the population observations fall within the given interval.

33) When a change has occurred in the mean of the process distribution, the result is referred to as

A. instability.
B. a cycle.
C. a trend.
D. a level shift.



34) When no point lies outside the control limits of a chart, we conclude that variation in the process is

A. due to special causes and there is enough evidence to infer that the process is under control.
B. due to common cause and there is enough evidence to infer that the process is out of control.
C. due to common cause and there is not enough evidence to infer that the process is out of control.
D. due to special causes and there is not enough evidence to infer that the process is out of control.



35) When the only sources of variation in a production process are caused by chance, the process is said to be

A. out of control but in balance.
B. under control.
C. out of control.
D. out of balance but under control

Explanation / Answer

(31)C. 350±16.38 (32)A. In repeated sampling, 95% of the intervals would contain the population parameter. (33)D. a level shift. (34)C. due to common cause and there is not enough evidence to infer that the process is out of control. (35)B. under control.

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