Question

The maintenance manager at a trucking company wants to build a regression model to forecast the time (in years) until the first engine overhaul based on four explanatory variables: (1) annual miles driven (in 1,000s of miles), (2) average load weight (in tons), (3) average driving speed (in mph), and (4) oil change interval (in 1,000s of miles). Based on driver logs and onboard computers, data have been obtained for a sample of 25 trucks. A portion of the data is shown in the accompanying table.

Time Until First Engine Overhaul	Annual Miles Driven	Average Load Weight	Average Driving Speed	Oil Change Interval
7.9	43.3	21	47	14
0.9	98.8	26	44	32
8.3	43.2	19	63	9
1.3	110.2	29	61	29
1.4	101.9	23	51	12
2.3	97	27	65	23
2.1	92.4	20	57	14
7.4	54.2	18	65	12
8.4	51.7	25	54	14
3.9	85.3	29	60	24
0.7	120.1	34	49	24
5.3	77.8	27	43	22
5.1	68.2	17	43	22
4.9	55	25	62	18
5.3	67.2	22	61	26
8.7	38.9	15	53	17
5.3	52.8	26	59	28
5.7	53.8	19	46	19
4.5	74.7	21	61	29
6.1	59	18	56	15
6.7	52.4	19	54	16
6.7	68.3	20	50	18
4.2	95	28	59	20
7.3	45.8	13	60	10
6	61.3	20	60	24

b. Estimate the regression model. (Negative values should be indicated by a minus sign. Round your answers to 4 decimal places.)

TimeˆTime^  = + Miles + Load + Speed + Oil

d. What is the predicted time before the first engine overhaul for a particular truck driven 60,000 miles per year with an average load of 23 tons, an average driving speed of 55 mph, and 21,000 miles between oil changes. (Round coefficient estimates to at least 4 decimal places and final answer to 2 decimal places.)

TimeˆTime^

years

Answer 1