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Chapter 8: Q. 32 (page 496)
confidence Find confidence interval using Table A or your calculator. Show your method.
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A quality control inspector will measure the salt content (in milligrams) in a random sample of bags of potato chips from an hour of production. which of the following would result in the smallest margin of error in estimating the mean salt content ?
(a) confidence; .
(b) confidence; .
(c) confidence; .
(d) confidence; .
(e) at any confidence level.
63. Give it some gas! Computers in some vehicles calculate various quantities related to performance. One of these is fuel efficiency, or gas mileage, usually expressed as miles per gallon (mpg). For one vehicle
equipped in this way, the miles per gallon were recorded each time the gas tank was filled and the computer was then reset. Here are the mpg values for a random sample of of these records:
Construct and interpret a confidence interval for the mean fuel efficiency M for this vehicle.
Scientists collect data on the blood cholesterol levels (milligrams per deciliter of blood) of a random sample of laboratory rats. A confidence interval for the mean blood cholesterol level is to . Which of the following would cause the most worry about the validity of this interval?
(a) There is a clear outlier in the data.
(b) A stemplot of the data shows a mild right skew.
(c) You do not know the population standard deviation .
(d) The population distribution is not exactly Normal.
(e) None of these would be a problem because the t procedures are robust.
Teens and their TV setsAccording to a Gallup Poll report, % of teens aged to have TVs in their rooms. Here is part of the footnote to this report:
These results are based on telephone interviews with a randomly selected national sample of teenagers in the Gallup Poll Panel of households, aged to . For results based on this sample, one can say . . . that the maximum error attributable to sampling and other random effects is percentage points. In addition to sampling error, question-wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.
(a) We omitted the confidence level from the footnote. Use what you have learned to determine the confidence level, assuming that Gallup took an SRS.
(b) Give an example of a “practical difficulty” that could lead to biased results for this survey.
56. The SAT again High school students who take the SAT Math exam a second time generally score higher than on their first try. Past data suggest that the score increase has a standard deviation of about points.
How large a sample of high school students would be needed to estimate the mean change in SAT score to within points with confidence? Show your work.
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