the level of significance is decreased, the interval for the population proportiona.becomes narrowerb.becomes widerc.does not changed.remains the sameANS: B25.The ability of an interval estimate to contain the value of the population parameter is described by the

26.After computing a confidence interval, the user believes the results are meaningless because the width of the interval is too large. Which one of the following is the best recommendation?27.If we change a 95% confidence interval estimate to a 99% confidence interval estimate, we can expect28.In general, higher confidence levels providea.wider confidence intervalsb.narrower confidence intervalsc.a smaller standard errord.unbiased estimatesANS: A29.An interval estimate is a range of values used to estimate30.In determining the sample size necessary to estimate a population proportion, which of the following information is notneeded?31.Whenever using the t distribution for interval estimation (when the sample size is very small), we mustassume that32.A sample of 20 items from a population with an unknown is selected in order to develop an interval estimate of . Which of the following is notnecessary?

a.We must assume the population has a normal distribution.b.We must use a t distribution.c.Sample standard deviation must be used to estimate .d.The sample must have a normal distribution.ANS: D33.A sample of 225 elements from a population with a standard deviation of 75 is selected. The sample mean is 180. The 95% confidence interval for is34.It is known that the variance of a population equals 1,936. A random sample of 121 has been taken from the population. There is a .95 probability that the sample mean will provide a margin of error of35.A random sample of 144 observations has a mean of 20, a median of 21, and a mode of 22. The population standard deviation is known to equal 4.8. The 95.44% confidence interval for the population mean is36.

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