Question

An investigator compares the durability a two different compounds used in the manufacture of a certain automobile brake lining. A sample of 212 brakes using compound 1 yields an average break life of 47895 miles. A sample of 180 brakes using compound 2 yields an average brake life of 49767 miles. Assume that the population standard deviation for compound 1 is 1590 miles, while the population standard deviation for compound 2 is 4152 miles. Determine the 90% confidence interval for the true difference between average lifetime for brakes using compound 1 and brakes using compound 2.

a) Find the point estimate for the true difference between the population means.

b) Find the margin of error of a confidence interval for the difference between the two population means. Round to 6 decimals.

c) Construct the 90% confidence interval. Round to 2
decimals.

Answer #1

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