AP Statistics Practice Test 20

1. Which of these explains why tshould be used instead of zfor inference procedures for means.

2. Which of the following is leastlikely to reduce bias in a sample survey?

3. In a study to determine whether there is a difference in color preferences for young children based on their gender, researchers had a random sample of children choose from a selection of toys that were identical except for their color. The table below shows the number of each color that was chosen by boys and by girls.

How many degrees of freedom should be used in a test of independence of gender and color preference?

4. A local library has a scanner to detect library materials that have not been checked out. Each item has a chip somewhere inside. Upon checkout, the chip is deactivated so the scanner will not set off the alarm. The scanner has a 98% chance of detecting an active chip (meaning the material has not been checked out) and setting off the alarm. The scanner also has a 3% chance of sounding the alarm when someone passes through without an active chip. It is estimated that 0.5% of library customers actually try to leave the library with an active chip. What is the probability that, if the alarm sounds, the patron leaving the library has an item with an active chip?

5. Which of the following is the best description of the power of a significance test?

6. A school board of a large school district is proposing a new dress code for students. Some students feel that this dress code unfairly targets female students. To see if there is a difference between boys and girls in their opposition to the new dress code, they conduct a poll of 60 randomly selected male and 70 randomly selected female high school students in the district. They find that 66 females oppose the dress code and 50 males oppose the dress code. Which of the following explains why a two-proportion z-test is not appropriate?

7. Researchers are conducting an experiment using a significance level of 0.05. The null hypothesis is, in fact, false. If they modify their experiment to use twice as many experimental units for each treatment, which of the following would be true?

8. A producer of skin care products has created a new formula for its cream to cure acne. To compare the effectiveness of the new cream to that of the old cream, it conducted a double-blind randomized experiment. Volunteers with acne tried the old formula on one side of their face and the new formula on the other, and which side got which formula was determined randomly. The response variable was the difference in the number of pimples (old formula - new formula). Which is the correct significance test to perform?

9. Smartphones with larger screens tend to be more expensive than smartphones with smaller screens. A random sample of currently available smartphones was selected. A 95% confidence interval for the slope of the regression line to predict price from screen size is (61, 542). Which of the following statements concerning this interval is correct?

10. In the 50 states of the United States, the financial climate for people living in retirement varies. Some states are very tax friendly to retirees. Other states are much less tax friendly to retirees. As a member of the Oregon state legislature, you wonder if Oregon's tax policies are driving older, retired people to move to other states. You have a cousin in Florida with the opposite idea-that the tax-friendly nature of Florida attracts more retirees. Each of you takes a random sample of the adults in your respective states and finds the statistics in the table below.

The 99% confidence interval for the difference in the mean age of adults in Oregon and adults in Florida is (-16.73, 8.69). Does this interval provide convincing evidence that the mean ages of adults in the two states differ?