b You can find the value of the correlation coefficient on the screen with linear regression results.
C
c Note that the price is in thousands of dollars and the mileage is in thousands of miles.
D
d Substitute the price for y in the equation for the line of the best fit.
E
e Substitute the mileage for x in the equation for the line of the best fit.
A
a y=- 0.2x+20
B
b r=- 0.968
C
c See solution.
D
d 22 500 miles
E
e $18 800
Practice makes perfect
a To perform a linear regression, we first have to enter the values into lists. Push STAT, choose Edit, and then enter the values in the first two columns.
To do a linear regression we push STAT, scroll right to CALC, and then choose the fourth option in the list, LinReg.
Therefore the correlation coefficient is approximately r=- 0.968. This tells us that correlation is both negative and very strong. We know that it is strong because it is extremely close to -1. A correlation of -1 would be a direct correlation explained by a line that goes through all of the points.
c Since the data shows the price in thousands of dollars and mileage in thousands of miles, the slope of - 0.2 means that for every 1 000 miles, a car is decreasing in value by $200. Meanwhile, the y-intercept has no interpretation because a used car cannot have the mileage equal to 0.
d In order to estimate the mileage of a car that costs $15 500 we have to substitute 15.5 for y in the equation for the line of the best fit.
