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MCS,PHD
Argosy University/ Phoniex University/
Nov-2005 - Oct-2011
Professor
Phoniex University
Oct-2001 - Nov-2016
12.    In a study of the lifetimes of electronic components, a random sample of 400 components are tested until they fail to function. The sample mean lifetime was 370 hours and the standard deviation was 650 hours. True or false:
a.   An approximate 95% confidence interval for the mean lifetime of this type of component is from
306.3 to 433.7 hours.
b.   About 95% of the sample components had life- times between 306.3 and 433.7 hours.
c.   If someone takes a random sample of 400 components, divides the sample standard deviation of their lifetimes by 20, and then adds and sub- tracts that quantity from the sample mean, there is about a 68% chance that the interval so con- structed will cover the mean lifetime of this type of component.
d.   The z table can’t be used to construct confidence intervals here, because the lifetimes of the compo-
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ii.   one-fourth as wide
iii.   one-half as wide
iv.   the same width
v.   twice as wide
vi.   four times as wide
vii.    eight times as wide
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