Florida International University

Business Statistics - STA 2023

Ms. Laura Reisert Instructor

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Chapter 2 Supplelmentary Exercises

1. A buyer for a lumber company must decide whether to buy a piece of land containing 5,000 pine trees. If 1,000 of the trees are at least 40 feet tall, the buyer will purchase the land; otherwise he will not. The owner of the land reports that the heights of the trees have a mean of 30 feet and a standard deviation of 3 feet. Based on this information, what is the buyer's decision?

2. Suppose a light bulb manufacturer claims that the mean lifetime of its bulbs is 35 hours. Assume you have prior knowledge that the bulb lifetimes have mound shaped distribution with a standard deviation of 5 hours.

a.) If the manufacturer's claim is true, approximately what percent of light bulbs will burn out in less than 20 hours?

b.) Suppose you randomly select one of the bulbs and it burns out in less than 20 hours. Do you suspect the manufacturer's claim is incorrect? EXPLAIN.

c.) What percentage of bulbs can be expected to burn out between 30 and 45 hours?

3. A professor believes that if a class is allowed to work on an examination as long as desired, the times spent by the students would be approximately mound shaped with a mean of 40 minutes and a standard deviation of 6 minutes. Approximately how long should be allotted for the examination if the professor wants almost all, say 97.5%, of the class to finish?