1. A random sample of 75 group leaders, supervisors, and similar personnel at General Motors revealed that, on average, they spent 7.5 years on the job before being promoted. The standard deviation of the sample was 1.7 years. Construct a 95 percent confidence interval.
2. A recent survey of 48 executives who were laid off during a recent recession revealed it took a mean of 28 weeks for them to find another position. The standard deviation of the sample was 6.8 weeks. Construct a 95 percent confidence interval for the population mean. Is it reasonable that the population mean is 28 weeks? Justify your answer.
3. The Human Relations Department of Electronics Inc. would like to include a dental plan as part of the benefits package. The question is: How much does a typical employee and his or her family spend per year on dental expenses? A sample of 48 employees reveals the mean amount spent last year was $1900, with a standard deviation of $700.
a. Construct a 95 percent confidence interval for the population mean.
b. The information from part (a) was given to the president of Electronics Inc. He indicated he could afford $1,700 of dental expenses per employee. Is it possible that the population mean could be $1,700? Justify your answer.