Example: Suppose that statistics quiz scores for a certain instructor are normally distributed with mean 70 and standard deviation 10. a. Find the probability that a sample of 25 quiz scores will have a mean score greater than 80. b. If a sample mean is chosen at random ,what is the probability that it will lie between 66.71 and 73.29 ? c. Find the 5th percentile of the class mean quiz scores. 7.2 Review Problems Example: In October 2004, the Gallup organization polled 1012 American adults, asking them, "Do you think there should or should not be a law that would ban the possession of handguns ,except by the police and other authorized persons .7" Of the 1012 randomly chosen respondents ,638 said that there should NOT be such a law. a. Check that the conditions have been met. b. Find the margin of error for 95%. c. Construct and interpret a 95% confidence interval for the population proportion of all American adults who think there should not be such a law. Example: Each year, billions of dollars are spent at theme parks owned by Disney, Universal Studios, Sea World, Busch Gardens, and others. A survey of 1233 people who took trips revealed that 111 of them included a visit to a theme park . a. Find the point estimate of the percentage of people who visit a theme park when they take a trip . b. Find 95% confidence interval estimate of the percentage of all people who visit a theme park when they take a trip. Example How many adults must be surveyed in order to be 95% confident that the sample percentage is in error by no more than three percentage points? 3. Use a recent result from the Census Bureau :66% of adults buy clothing online . b. Assume that we have no prior information suggesting a possible value of the proportion Example How many adults must be surveyed in order to be 95% confident that the sample percentage is in error by no more than three percentage points