AP Stats Inferences for Means

A manufacturer claims that his tires average 40,000 miles. A test on 25 tires reveals that the mean life of a tire is 39,750 miles, with a standard deviation of 387 miles. You do not think that the tires average 40,000 miles. Test the Manufacturer’s claim at α = .01. Write the null and alternative hypothesis.

A manufacturer claims that his tires average 40,000 miles. A test on 25 tires reveals that the mean life of a tire is 39,750 miles, with a standard deviation of 387 miles. You do not think that the tires average 40,000 miles. Test the Manufacturer’s claim at α = .01. Calculate the test-statistic

• z = -3.23

• z = -0.65

• t = -3.23

• t = -0.65

A manufacturer claims that his tires average 40,000

miles. A test on 25 tires reveals that the mean life of a tire

is 39,750 miles, with a standard deviation of 387 miles. You do not think that the tires average 40,000 miles.

Test the Manufacturer’s claim at α = .01.

Determine your conclusion.

• Reject Ho

• Reject Ha

• Fail to reject Ho

• Fail to reject Ha

A box of Raspberry Crunch cereal contains a mean of 13 ounces with a standard deviation of 0.5 ounces.  The distribution of the contents of cereal boxes is approximately Normal.  The cereal company is afraid the boxes being over filled.  Suppose they get a random sample of 25 boxes, and find a mean of 13.2 and a standard deviation of 0.154.  Does this give evidence that the boxes are being overfilled?

• sample t-test

• sample t-test

• proportion z-test

• chi-squared GOF test

An IQ test was given to a simple random sample of 75 students at a certain college. The sample mean score was 105.2. Scores on this test are known to have a standard deviation of 10. It is desired to construct a 90% confidence interval for the mean IQ scores of the students at the college.

Find the critical value.

• 0.90

• 1.155

• 1.645

• ±1.645

The football coach randomly selected ten players and timed how long each player took to perform a certain drill. The times (in minutes) were: 13.2,  5.1,  7.5,  8.0,  12.7,  7.6,  13.8,  14.5,  7.7, and 10.5.  Determine a 95 percent confidence interval for the mean time for all players.

• 12.30 < μ < 7.82

•  7.82 < μ < 12.30

• 7.72 < μ < 12.40

• 12.40 < μ < 7.72

Two important sample statistics are…

We check the same conditions in both inference tests for mean.

• True

• False

Which of the following is the best estimate of the standard deviation of the distribution in the figure?

• 18

• 9

• 54

• 97

• 106

A company determines the mean and standard deviation of the employees' salaries in one year. What is the best description of the standard deviation?

• Approximately the median distance between the individual salaries of employees and the mean of every employee's salary.

• The amount of money separating the highest salary from the lowest salary when considering the middle 50% of the distribution.

• The amount of money separating the highest salary from the lowest salary when considering all employees.

• The distance between the salary of an employee and the mean salary of all the employees.

• Approximately the mean distance between the individual salaries of employees and the mean of all employees' salaries.