Statistic

9. One model of an imported automobile is known to have defective seat belts. An extensive study found that 17% of the seat belts were incorrectly installed at the factory. A car dealer has just received a shipment of 196 of this model car. What is the probability that in this shipment 22 or fewer have defective seat belts? CCF ? F and U ? zinterval ? final answer? 10. The scores of students on the ACT college entrance examination in a recent year had the normal distribution with ,u : 20.4 and standard deviation 0' :5 .3. a. What is the shape of the distribution for samples of 30 ACT scores? b. What are the mean and standard deviation of the average ACT score, :3 for a sample of 30 students? c. What is probability that the average ACT score of 30 students is 24 or higher? 11. A hospital is trying to cut down on emergency room wait times. It is interested in the amount of time patients must wait before being called back to be examined. An investigation committee randomly surveyed 70 patients. The sample mean was 1.5 hours. Construct a 95% confidence interval for the population mean time spent waiting. (Use 0 : 0.5) Z : Error : CI: 12. A manufacturer of college textbooks is interested in estimating the strength of the bindings produced by a particular binding machine. Strength can be measured by recording the force required to pull the pages from the binding. If this force is measured in pounds, how many books should be tested to estimate with 92% confidence to within 0.1 1b, the average force required to break the binding? Assume that G is known to be 0.3 lb. 22 11