Question

An investigator compares the durability of two different compounds used in the manufacture of a certain automobile brake lining. A sample of 255 brakes using Compound 1 yields an average brake life of 48,859 miles. A sample of 298 brakes using Compound 2 yields an average brake life of 49,062 miles. Assume that the population standard deviation for Compound 1 is 4700 miles, while the population standard deviation for Compound 2 is 2759 miles. Determine the 90% confidence interval for the true difference between average lifetimes for brakes using Compound 1 and brakes using Compound 2.

Step 2 of 3 :  

Calculate the margin of error of a confidence interval for the difference between the two population means. Round your answer to six decimal places.

Step 3 of 3:

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

Answer 1