1. The American Management Association wishes to have information on the mean income of store managers in the retail industry. A random sample of 256 managers reveals a sample mean of $45,420. the standard deviation of this population is $2050. You need to construct 90%, 95% and 99% CIs for the mean income of the population. Which CI is the widest?

A. 90% Cl

B. 95% Cl

C. 99% Cl

D. not enough information

2. A tire manufacturer wishes to investigate the tread life of its tires. A sample of 10 tires driven 50,000 miles revealed a sample mean of 0.32 inch of tread remaining with a standard deviation of 0.09 inch. To construct a 95 percent Confidence Interval for the population mean, you will need 97.5-percentile of a ____.

A. Standard normal distribution (z distribution).

B. t distribution with degree of freedom 10.

C. t distribution with degree of freedom 9.

3. The union representing the Bottle Blowers of America (BBA) is considering a proposal to merge with the Teamsters Union. According to BBA union bylaws, at least three-fourths of the union membership must approve any merger. A random sample of 2,000 current BBA members reveals 1,600 plan to vote for the merger proposal. What is the estimate of the population proportion?

4. The Quality Assurance Department for Cola, Inc., maintains records regarding the amount of cola in its Jumbo bottle. The actual amount of cola in each bottle is critical, but varies a small amount from one bottle to the next. Cola, Inc., does not wish to underfill the bottles. On the other hand, it cannot overfill each bottle. Its records indicate that the amount of cola follows the normal probability distribution. The mean amount per bottle is 31.2 ounces and the population standard deviation is 0.4 ounces. According to the Central Limit Theorem, you determine the sampling mean follows the Normal distribution, with mean of _____ and standard deviation of _____.

5. There is a family of t distributions. All t distributions have a mean of 0, but their standard deviations differ according to the sample size, n, or more precisely, the degree of freedom n-1. True or False?

6. The t distribution is more spread out and flatter at the center than the standard normal distribution As the sample size increases, however, the t distribution approaches the standard normal distribution. True or False?

7. t distribution is a continuous distribution. True or False?

8. t distribution is bell-shaped and symmetrical. True or False?

9. If random variables X1, X2, X3, ... Xn follows Uniform(0,10) distribution, the mean (of X1, X2, X3, ... Xn) will be approximately normally distributed. This approximation improves with larger samples. True or False?

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