Exam 21: What Is a Confidence Interval

The student newspaper at a college asks a simple random sample of 250 undergraduates, "Do you favor eliminating supplemental fees for lab courses?" In all, 150 of the 250 are in favor of eliminating such fees. To estimate p, you will use the proportion = 150/250 of your sample who favored eliminating supplemental fees for lab courses. The number is a

The student newspaper at a college asks a simple random sample of 250 undergraduates, "Do you favor eliminating supplemental fees for lab courses?" In all, 150 of the 250 are in favor of eliminating such fees. Suppose that (unknown to you) 55% of all undergraduates favor eliminating supplemental fees for lab courses. If you took a very large number of simple random samples of size n = 250 from this population, the sampling distribution of the sample proportion p would be approximately normal with

In a simple random sample of 144 households in a city in Kentucky, the average number of children in these households was 1.12 children. The standard deviation from this sample was 2.40 children. A 90 percent confidence interval for the mean number of children in all households in this city is: