# Confidence Interval and Sample Size in HR Departments

1.) A sample of 35 different HR departments found that employees worked an average of 240.6 days a year. If the population standard deviation is 18.8 days, find the 90% confidence interval for the average number of days ? worked by all employees of these HR departments.

A) 230.9 < ? < 250.3

B) 236.8 < ? < 244.4

C) 232.4 < ? < 248.8

D) 235.4 < ? < 245.8

2.) A study of 35 brown gerbils showed that their average weight was 4.7 ounces. The standard deviation of the population is 0.7 ounces. Which of the following is the 99% confidence interval for the mean weight per brown gerbils?

A) 4.09 < ? < 5.31

B) 4.39 < ? < 5.01

C) 4.42 < ? < 4.98

D) 4.55 < ? < 4.85

3.) A study of lemon trees found that the average number of lemons per tree was 725. The standard deviation of the population is 70 lemons per tree. A scientist wishes to find the 80% confidence interval for the mean number of lemons per tree. How many trees does she need to sample to obtain an average accurate to within 16 lemons per tree?

A) 21

B) 20

C) 32

D) 14

4.) In a study using 10 samples, and in which the population variance is unknown, the distribution that should be used to calculate confidence intervals is

A) a t distribution with 10 degrees of freedom.

B) a t distribution with 11 degrees of freedom.

C) a t distribution with 9 degrees of freedom.

D) a standard normal distribution

5.) A potato chip manufacturer samples 13 bags of potato chips off the assembly line and weighs their contents. If the sample mean is 14.2 oz. and the sample standard deviation is 0.60 oz., find the 95% confidence interval of the true mean.

A) 11.6 < ? < 16.8

B) 13.8 < ? < 14.6

C) 12.9 < ? < 15.5

D) 14.0 < ? < 14.4

6.) The winning team's score in 7 high school basketball games was recorded. If the sample mean is 62.3 points and the sample standard deviation is 13.0 points, find the 98% confidence interval of the true mean.

A) 50.9 < ? < 73.7

B) 31.4 < ? < 93.2

C) 46.9 < ? < 77.7

D) 57.4 < ? < 67.2

7.) If a population has a standard deviation of 10, what is the minimum number of samples that need to be averaged in order to be 95% confident that the average of the means is within 2 of the true mean?

A) 20

B) 97

C) 191

D) 10

8.) A computer analyst conducted a study of the access speed of 45 hard drives and concluded that her maximum error of estimate was 28. If she were to conduct a second study to reduce the maximum error of estimate to 7, about how many hard drives should she include in her new sample?

A) 90

B) 180

C) 720

D) 45

9.) If pË? is 0.76, then qË? is _________.

A) 0.31

B) 0.24

C) 0.50

D) 0.76

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#### Solution Summary

The solution provides answers to multiple choice questions on confidence interval and sample size. Workings in excel spreadsheet is also included.