The computer science department wants to estimate the average length of time it takes students to complete a computer project correct to within 5 hours with probability 0.96.  They do not have an estimate of the standard deviation of the times, but they remember that last year the shortest time needed to complete the project was 6 hours and the longest time was 36 hours.  Given this information, find an appropriate estimate of the standard deviation of the length of time required to complete the computer project and then find the sample size needed to estimate the average length of time it takes students to complete the computer project correct to within 5 hours with probability 0.96.

The mean length of time required to complete the Columbus Marathon was 4.5 hours and the standard deviation of the times was 0.50 hours.  Assume that the racing times were approximately normally distributed.  Only 10% of the runners would be expected to complete the race in less than x hours.  Find the value of x.

A bottling company needs to produce bottles that will hold 12 ounces of liquid for a local beer maker.  Periodically, the company receives complaints that their bottles are not holding enough liquid.  To test this claim, the bottling company randomly samples 15 bottles and finds the average amount of liquid held by the 15 bottles is 11.90 ounces and the standard deviation is 0.20 ounces. Suppose the test results indicated that the null hypothesis should be rejected, and, as a result, the company shut down their machine for inspection.  However, a thorough examination revealed that the machine was filling the bottles correctly.  From a statistical point of view, which one of the following is true?

Which of the following probabilities for the sample points A, B, and C could be true if A, B, and C are the only sample points in an experiment?

The body weight in pounds (variable X) and fleece weight in pounds (variable Y) of a random sample of four ewes are as follows: Body weight, lb (X)            Fleece weight, lb (Y)           140                                            9           145                                          10           155                                          10           160                                          12                                                                                      Calculate the variance of fleece weight.

A ________ ________ error occurs if we reject a null hypothesis when it is true.

Find the standard deviation of a binomial probability distribution with a sample size of n = 20 and a probability of success of 0.40.

Suppose that a random sample of 100 measurements is selected from a population with a mean µ = 200 lb and a variance σ2 = 1,600 lb2.  What is the mean and standard deviation of the sampling distribution of the sample mean?

A plant scientist wants to determine the average yield (in bushels per acre) of brand X corn in Ohio.  Five thousand Ohio corn fields are planted using brand X.  The plant scientist is able to obtain data for the yields of 500 of these 5,000 fields.  The average yield of these 500 fields planted to brand X is 175 bushels per acre.  What does the value of 175 bushels per acre represent?

It is desired to estimate the average total compensation of CEO’s in the service industry.  Data were collected from 18 CEO’s and a 97% confidence interval was calculated to be ($2,181,260,  $5,836,180).  Which one of the following interpretations is correct?