Two popular brands of tires for tractor-trailers are the Puma and the Eternal. Maya is a buyer for a major shipping company and wants to estimate the difference between the mean distance(in thousands of

km

)driven on Puma tires before they need to be replaced and the mean distance(in thousands of

km

)driven on Eternal tires before they need to be replaced.

In the company's testing lab, Maya tests a random sample of

14

Puma tires and a random sample of

15

Eternal tires. (These samples are chosen independently.) For each tire she logs the distance driven(in thousands of

km

)before the tire would need to be replaced. These data are shown in the table.

	Distances (in thousands of km )
Puma	55.2 , 55.6 , 56.0 , 52.6 , 54.8 , 53.3 , 54.6 , 53.3 , 47.9 , 54.2 , 52.6 , 58.6 , 57.4 , 57.0
Eternal	48.0 , 45.0 , 43.4 , 73.0 , 52.7 , 47.3 , 45.1 , 31.1 , 39.1 , 53.0 , 63.0 , 51.6 , 56.6 , 56.1 , 52.0

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Assume that the two populations of distances driven are approximately normally distributed. Let

1

be the population mean distance(in thousands of

km

)driven on Puma tires before they need to be replaced. Let

2

be the population mean distance(in thousands of

km

)driven on Eternal tires before they need to be replaced.

Construct a

90%

confidence interval for the difference

12

.Then find the lower and upper limit of the

90%

confidence interval. Carry your intermediate computations to three or more decimal places. Round your answers to two or more decimal places. (If necessary, consult alist of formulas.)

Lower limit: Upper limit: