He decides to explore this phenomenon and asks 15 of

He decides to explore this phenomenon, and asks 15 of his neighbors how
many times they wash their cars each year and how much they paid in car repair costs last year.
His results are in the table below:
Mean Standard deviation
x = number of car washes per year 6.4 3.78
y = repairs costs for last year $955.30 $323.50
The correlation for these to two variables is r = -0.71
16. Find the equation of the least-squares regression line (with y as the response variable).
17. What percentage of the variation in repair costs can be explained by the number of times per
year a car is washed?
18. Based on these data, can we conclude that washing your car frequently will reduce repair
costs? Explain.

Test 3B AP Statistics Name:
Part 1: Multiple Choice. Circle the letter corresponding to the best answer.
Questions 1 and 2 refer to the following information:
For children between the ages of 18 months and 29 months, there is an approximately linear
relationship between height and age. The relationship can be represented by
ˆ y = 64.93 + 0.63 x , where y represents height (in centimeters) and x represents age (in months).
1. Joseph is 22.5 months old. What is his predicted height?
87.40
2. Loretta is 20 months old and is 80 centimeters tall. What is her residual?
77.53
3. You have data for many families on the parents’ income and the years of education their
eldest child completes. Your initial examination of the data indicates that children from
wealthier families tend to go to school for longer. When you make a scatterplot,
4. A community college announces that the correlation between college entrance exam grades and
scholastic achievement was found to be –1.08. On the basis of this you would tell the college
that
(a) the entrance exam is a good predictor of success.
(b) the exam is a poor predictor of success.
(c) students who do best on this exam will be poor students.
(d) students at this school are underachieving.
(e) the college should hire a new statistician.
126 The Practice of Statistics, 4/e- Chapter 3 © 2011 BFW Publishers