07-13-12
Exercise
in confidence intervals for the mean (standard deviation unknown or sample size
less than 30)
1.
Find the ta/2 value for 95% confidence interval when the sample size is 22.
2.
Ten randomly selected automobiles were stopped and the tread from right of the
tire was measured. The mean was 0.32
inch and the standard deviation was 0.08 inch.
Find the 95%confidence interval of the mean depth. Assume that the variable is normally
distributed.
3.
A recent study of 28 city residents
showed that the mean of the time they had lived at their present address was
9.3 years. The standard deviation of the
sample was 2 years. Find the 90%
confidence interval of the true mean.
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