AP Stats Review

With practice, people become faster at solving a certain type of mathematical puzzle. Fourteen college students were allowed to practice completing a certain type of mathematical puzzle for different amounts of time. Afterwards, each student’s completion time on a new puzzle was measured. The Residual plot for regression of Completion Time on Practice Time is shown below. Which of the following is correct?

• There is a no relationship between Practice Time and Puzzle Completion Time.

• This regression equation would likely overestimate the Puzzle Completion Time for 175 minutes of practice time.

• There is a non-linear relationship between Practice Time and Puzzle Completion Time.

For the density curve shown, which of the following statements is true?

• The mean is larger than the median.

• The proportion of outcomes between 0.2 and 0.5 is equal to 0.3.

• The total area under the curve is greater than 1.

• The proportion of outcomes greater than 1.5 is equal to 0.25.

The weights of cockroaches living in a university dormitory follow a Normal distribution with mean 80 grams and standard deviation 5 grams. The percentage of cockroaches having weights between 72 grams and 88 grams must be

• less than 68%.

• between 68% and 95%.

• between 95% and 99.7%.

• between 99.7% and 100%.

Scores on the American College Testing (ACT) college entrance exam follow a Normal distribution with mean 18 and standard deviation 6. Lisa’s standardized score on the ACT was z = -0.7. What was her actual ACT score?

• 4.2

• 13.8

• 17.3

• 22.2

The lifetime of 9-volt battery in constant use has an approximately Normal distribution with a mean of 516 hours and a standard deviation of 20 hours. Which of the following best describes the distribution of standard scores for the lifetimes of such batteries?

• Exactly Normal, with mean 0 and standard deviation 1.

• Approximately Normal, with mean 0 and standard deviation 1.

• Approximately Normal, with mean 1 and standard deviation 1.

In the class of 2016, more than 1.6 million students took the SAT. The distribution of scores on the math section (out of 800) follows an approximately Normal distribution with a mean of 508 and standard deviation of 110. About what percent of students who took the SAT scored less than 350 on the math section?

• about 1.4%

• about 7.5%

• about 12%

A maple sugar manufacturer wants to estimate the average trunk diameter of Sugar Maples trees in a large forest. There are too many trees to list them all and take a SRS, so he divides the forest into several hundred 10 meter by 10 meter plots, selects 25 plots at random, and measures the diameter of every Sugar Maple in each one. This is an example of a

• multistage sample.

• stratified sample

• simple random sample.

• cluster sample.

• convenience sample.

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.

The equation of the LSRL for the points on a scatterplot is ŷ = 5.3-0.23x. What is the residual for the point (5, 4)?

• -0.15

• 0.15

• 1

• 0.62

• 0.85