Chapter 7: Problem 7
You are receiving a large shipment of batteries and want to test their lifetimes. Explain why you would want to test a sample of batteries rather than the entire population.
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Chapter 7: Problem 7
You are receiving a large shipment of batteries and want to test their lifetimes. Explain why you would want to test a sample of batteries rather than the entire population.
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In a die roll, 3 and 6 are multiples of 3 and \(1,2,4\), and 5 are not multiples of \(3 .\) Consider 90 rolls of a die on a random basis. a. From how many outcomes of the 90 rolls would you expect to get multiples of 3 , on average? b. If you actually counted, would you get exactly the number you predicted in part a? Explain.
Natural habitats must be protected to maintain the ecological balance. According to indexmundi.com's survey in 2010, about \(26 \%\) of the land in Brazil is a habitat-protected area. Suppose a geologist randomly selects 200 regions to study soil types found in the country. Use the Central Limit Theorem (and the Empirical Rule) to find the approximate probability that the proportion of protected regions is more than one standard error from the population value of \(0.26\). The conditions for using the Central Limit Theorem are satisfied because the sample is random; the population is more than 10 times \(1000 ; n\) times \(p\) is 52, and \(n\) times ( 1 minus \(p)\) is 148, and both are more than 10 .
Suppose you want to estimate the mean weight of all the people in your locality. You set up a table outside a park asking for volunteers to tell you their weights. Do you think you would get a representative sample? Why or why not?
Suppose you go to a department store where one can shop both in-store and online. You want to know the average purchase volume per customer. You walk around the store asking the customers their order values. Would this result in a biased sample?
a. If a rifleman's gunsight is adjusted correctly but he has shaky arms, the bullets might be scattered widely around the bull's-eye target. Draw a sketch of the target with the bullet holes. Does this show variation (lack of precision) or bias? b. Draw a second sketch of the target if the shots are unbiased and have precision (little variation). The rifleman's aim is not perfect, so your sketches should show more than one bullet hole.
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