STA113: Probability and Statistics in Engineering

Homework #9

Due: Friday, Apr 17

Problems

All problems below concern the following data, taken from the Consumers Union automobile fuel data set:

	Cyl	Wgt	Disp	Mge	Fuel	Type
Chevrolet Camaro	8	3320	305	20	5.000	Sporty
Chevrolet Beretta	4	2655	133	26	3.846	Compact
Chevrolet Caprice	8	3855	305	18	5.556	Large
Chevrolet Limina APV	6	3195	151	18	5.556	Van

Problem 1

a)	Plot Mileage vs. Weight for these four data.
b)	Find the regression intercept and slope coefficients b0 and b1 (use Minitab)
c)	Add the regression line to your plot in a)
d)	Make a (point) prediction of the mileage for a 3000lb Chevrolet
e)	Make a (point) prediction of the mileage for a 5000lb Chevrolet

Problem 2

a)	Plot Fuel vs. Weight for these four data.
b)	Find the regression intercept and slope coefficients b0 and b1 (use Minitab)
c)	Add the regression line to your plot in a)
d)	Make a (point) prediction of the mileage for a 3000lb Chevrolet
e)	Make a (point) prediction of the mileage for a 5000lb Chevrolet

Problem 3

In Problem 1 and Problem 2 you made two different predictions of the mileage for a 3000lb car. Which do you think is better, and why?

The numbers b0, b1 you found above (using Minitab) minimize SOMETHING. What? Describe in words and in a picture on your plot just what minimization property the regression line has.

Problem 5

Give 90% PREDICTION intervals for the fuel consumed by a 3000lb Chevrolet automobile and by a 5000lb Chevrolet in traveling 100mi. Convert these same intervals into 90% prediction intervals for the gas mileage of these cars. Explain (in words, not formulas) why the intervals for the 5000lb automobile are wider than those for the 3000lb car.