In a manufacturing process a random sample of 9 bolts manufactured has a mean length of 3 inches with a variance of .09. What is the 90% confidence interval for the true mean length of the bolt?

A. 2.8355 to 3.1645

B. 2.5065 to 3.4935

C. 2.4420 to 3.5580

D. 2.8140 to 3.8160

E. 2.9442 to 3.0558

In a manufacturing process a random sample of 9 bolts manufactured has a mean length of 3 inches with a variance of .09. What is the 90% confidence interval for the true mean length of the bolt? A. 2.8355 to 3.1645 B. 2.5065 to 3.4935 C. 2.4420 to 3.5580 D. 2.8140 to 3.8160 E. 2.9442 to 3.0558 8. In a manufacturing process a random sample of 9 bolts manufactured has a mean length of 3 inches with a standard deviation of .3 inches. What is the 95% confidence interval for the true mean length of the bolt?

A. 2.804 to 3.196

B. 2.308 to 3.692

C. 2.770 to 3.231

D. 2.412 to 3.588

E. 2.814 to 3.186

A company is interested in estimating , the mean number of days of sick leave taken

by its employees. The firm's statistician randomly selects 100 personnel files and notes the

number of sick days taken by each employee. The sample mean is 12.2 days and the sample

standard deviation is 10 days. How many personnel files would the director have to select in

order to estimate to within 2 days with a 99% confidence interval?

A. 2

B. 13

C. 136

D. 165

E. 166

Find the 99 percent confidence interval for p when = .2, and n = 100.

A. [.068 .332]

B. [.097 .303]

C. [.159 .241]

D. [.147 .253]

Assume that the distribution of IQ is normal, with mean 100 and standard deviation 10. Find P(IQ <120).

A. .0228

B. .0456

C. .9544

D. .9772

If the continuous random variable X is normal, with mean and standard deviation s. Find

P( -2s

A. 0.5774

B. 0.6827

C. 0.8647

D. 0.9544

A random sample of size 30 from a normal population yields X = 32.8 with a population standard deviation of 4.51. Construct a 95 percent confidence interval for .

A. [23.96 41.64]

B. [32.04 33.56]

C. [31.45 34.15]

D. [31.19 34.41]

In a manufacturing process, we are interested in measuring the average length of a certain type of bolt. Past data indicates that the standard deviation is .25 inches. How many bolts should be sampled in order to make us 95% confident that the sample mean bolt length is within .02 inches of the true mean bolt length?

A. 421

B. 423

C. 599

D. 601

A random sample of size 30 from a normal population yields = 32.8 with a population standard deviation of 4.51. Construct a 95 percent confidence interval for .

A. [23.96 41.64]

B. [32.04 33.56]

C. [31.45 34.15]

D. [31.19 34.41]

The next three questions are based on the following paragraph.

A large hospital wholesaler, as part of an assessment of workplace safety, gave a random sample of 54 of its warehouse employees a test (measured on a 0 to 100 point scale) on safety procedures. For that sample of employees, the mean test score was 75 points, with a sample standard deviation of 15 points. Determine and interpret a 95% confidence interval for the mean test score of all the company's warehouse employees. (Please keep at least four decimal places).

To construct the 95% confidence interval, we should: A. use t-value 1.669 from the t table, because we have the sample standard deviation. B. use t-value 2.006 from the t table, because we have the sample standard deviation. C. use z-value 2.576 from the z table, because we have the population standard deviation. D. use z-value 1.960 from the z table, because we have the population standard deviation.

The 95% confidence interval is:

A. [71.8706, 78.1294]

B. [72.0687, 77.9412]

C. [71.2537, 78.7463]

D. [70.9053, 79.0947]

We can interpret the interval in the following manner:

A. We are 5% confident that the population mean test score is covered by the interval.

B. We are 95% confident that the population mean test score is covered by the interval.

C. We are 99% confident that the population mean test score is NOT covered by the interval.

D. The length of the interval is 95% of one.