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 lifetimes 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 subtracts that quantity from the sample mean, there is about a 68% chance that the interval so constructed 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 components don’t follow the normal curve. e) About 68% of the components had lifetimes in the interval 370 ± 650 hours.
In a study of the lifetimes of electronic components, a random sample of 400 components
are tested until they fail to
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 lifetimes 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 subtracts that quantity from the
sample mean, there is about a 68% chance that the interval so constructed 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 components don’t follow the normal curve.
e) About 68% of the components had lifetimes in the interval 370 ± 650 hours.
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