Posted by **Jason L** on Monday, February 26, 2007 at 3:52pm.

It is known that the amount of time needed to change the oil in a car is normally distributed with a standard deviation of 5 minutes. A random sample of 100 oil changes yielded a sample mean of 22 minutes. Compute the 99% confidence interval estimate of the mean of the population.

Also determine the necessary sample size if you wish to be 99% confident and can tolerate an error of 1 minute.

Part 3 - With a sample size not exceeding 150 but everything else staying the same, what confidence level can be achieved?

95

96

97

98

still 99

This was answered in a previous post. For part 3, you can probably still use the same confidence interval.

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