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Chapter 8: Q.31 (page 496)
98% Confidence find for aconfidence interval using table A or tour calculator. show your method.
The value of is
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Use Table B to find the critical value t* that you would use for a confidence interval for a population mean M in each of the following situations. If possible, check your answer with technology.
(a) A 98% confidence interval based on observations.
(b) A confidence interval from an SRS of observations.
(c) A confidence interval from a sample of size.
62. Blink When two lights close together blink alternately, we “see” one light moving back and forth if the time between blinks is short. What is the
longest interval of time between blinks that preserves the illusion of motion? Ask subjects to turn a knob that slows the blinking until they “see” two lights rather than one light moving. A report gives the results in the form “mean plus or minus the standard error of the mean.” Data for subjects are summarized as (in milliseconds).
(a) Find the sample standard deviation for these measurements. Show your work.
(b) Explain why the interval is not a confidence interval.
64. Vitamin C content Several years ago, the U.S. Agency for International Development provided metric tons of corn-soy blend (CSB) for
emergency relief in countries throughout the world. CSB is a highly nutritious, low-cost fortified food. As part of a study to evaluate appropriate vitamin C levels in this food, measurements were taken on samples of CSB produced in a factory. The following data are the amounts of vitamin C,
measured in milligrams per grams (mg/100 g) of blend, for a random sample of size from one production run:
Construct and interpret aconfidence interval for the mean amount of vitamin C M in the CSB from this production run.
61. Willows in Yellowstone Writers in some fields summarize data by giving and its standard error rather than and . Biologists studying willow trees in Yellowstone National Park reported their results in a table with columns labeled . The table entry for the heights of willow trees (in centimeters) in one region of the park was The researchers measured a total of trees.
(a) Find the sample standard deviation for these measurements. Show your work.
(b) Explain why the given interval is not a confidence interval for the mean height of willow trees in this region of the park.
The AP Statistics class in Exercise also asked an SRS of boys at their school how many shoes they have. A confidence interval for the difference in the population means (girls – boys) is to . Interpret the confidence interval and the confidence level.
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