NOTE: Use t-distribution, when n is less than 30, or? unknown or both cases happen. 1. When a 99% confidence interval is

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NOTE Use t-distribution, when n is less than 30, or unknown

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NOTE: Use t-distribution, when n is less than 30, or ? unknown or both cases happen. 1. When a 99% confidence interval is calculated instead of a 95% confidence interval with n being the same, the maximum error of estimate will be (a) Smaller (b) larger (c) the same (d) it cannot be determined

2. A random sample of 49 shoppers showed that they spend an average of $23.45 per visit at a mall bookstore. The standard deviation of the population is $2.80. Find the 90% confidence interval of the true mean.

3. The average weigh of 40 randomly minivans was 4150 pounds. The standard deviation was 480 pounds. Find the 99% confidence interval of the true mean weight of the minivans.

4. In a study of 10 insurance sales representatives from a certain large city, the average age of the group was 48.6 years and the standard deviation was 4.1 years. Find the 95% confidence interval of the population mean age of all insurance sales representatives in that city.

5. In a hospital, a sample of 8 weeks was selected, and it was found that an average of 438 patients was treated in the emergency room each week. The standard deviation was 16. Find the 99% confidence interval of the true mean.

6. A university dean wishes to estimate the average number of hours that the freshmen study each week. The standard deviation from a previous study is 2.6 hours. How large a sample must be selected if he wants to be 99% confident of finding whether the true mean differs from a sample mean by 0.5 hour?

7. A recent study of 75 workers found that 53 people rode the bus to work each day. Find the 95% confidence interval of the proportion of all workers who rode the bus to work.

8. In a study of 150 accidents that required treatment in an emergency room, 36% involved children under 6 years of age. Find the 90% confidence interval of the true proportion of accidents that involve children under the age of 6.

9. In a survey of 1004 individuals, 442 felt that President Barack Obama spent too much time away from Washington. Find a 95% confidence interval for the true proportion.

10. The data below represent children’s animated film lengths in minutes. Estimate the true length of all children’s animated films with 95% confidence. 93 83 76 92 77 81 78 100 78 76 75