AP Statistics
Chapter 8 Confidence Intervals
Extra Practice Problems
Multiple Choice
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Free-Response Questions
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2.) A company that produces pens wants to know how long its pens can go until the ink runs out. A
random sample of 49 pens is tested, and the mean operating time is found to be 188 hours with a
standard deviation of 6 hours.
(A) Create a 95% confidence interval for the true mean time of all pens.
(B) The head manufacturer of the company claims that this mean will operate at a mean of 190 hours.
Does the company’s claim seem justified? Explain.
(C) What is the probability that another random sample of 49 pens will have an average of 190 hours
or more?