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Chapter 7: Q.8 (page 429)
How tall? A random sample of female college students has a mean height of inches, which is greater than the -inch mean height of all adult American women.
The value of
Statistic
Parameter .
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Songs on an iPod David's iPod has about songs. The distribution of the play times for these songs is heavily skewed to the right with a mean of seconds and a standard deviation of seconds.
(a) Explain why you cannot safely calculate the probability that the mean play time is more than minutes seconds for an SRS of songs.
(b) Suppose we take an SRS of songs instead. Explain how the central limit theorem allows us to find the probability that the mean playtime is more than seconds. Then calculate this probability. Show your work.
The gypsy moth is a serious threat to oak and aspen trees. A state agriculture department places traps throughout the state to detect the moths. When traps are checked periodically, the mean number of moths trapped is only but some traps have several moths. The distribution of moth counts is discrete and strongly skewed, with standard deviation.
(a) What are the mean and standard deviation of the average number of moths intraps?
(b) Use the central limit theorem to help you find the probability that the average number of moths in traps is greater than.
A large company is interested in improving the efficiency of its customer service and decides to examine the length of the business phone calls made to clients by its sales staff. A cumulative relative frequency graph is shown below from data collected over the past year. According to the graph, the shortest of calls will take how long to complete?
(a) Less than minutes.
(b) At least minutes.
(c) Exactly minutes.
(d) At least minutes.
(e) Less than minutes.
Making auto parts grinding machine in an auto parts plant prepares axles with a target diameter millimeters (mm). The machine has some variability, so the standard deviation of the diameters is . The machine operator inspects a random sample of axles cach hour for quality control purposes and records the sample mean diameter ,how many axles would you need to sample if you wanted the standard deviation of the sampling distribution to be?justify your answer.
On Tuesday, the bottles of Arizona Iced Tea filled in a plant were supposed to contain an average of ounces of iced tea. Quality control inspectors sampledbottles at random from the day鈥檚 production. These bottles contained an average of ounces of iced tea.
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