Question

An investigator compares the durability of two different
compounds used in the manufacture of a certain automobile brake
lining. **A sample of 121 brakes** using Compound 1
yields an **average brake life of 39,122 miles**.
**A sample of 163 brakes** using Compound 2 yields an
**average brake life of 48,271 miles**. Assume that
**the population standard deviation for Compound 1 is 3175
miles**, **while the population standard deviation for
Compound 2 is 1335 miles**. **Determine the 98%
confidence interval for the true difference between average
lifetimes for brakes using Compound 1 and brakes using Compound
2.**

**Step 1 of 3: Find the point estimate for the true
difference between the population means.**

**Step 2 of 3: Find the margin of error of a confidence
interval for the difference between the two population means. Round
to 6 decimals.**

**Step 3 of 3: Construct the 98% confidence interval.
Round to 2 decimals.**

Answer #1

The statistical software output for this problem is:

Hence,

Step - 1: point estimate = -**9149**

Step - 2: Margin of error = (-8903.3144 + 9394.6856)/2 =
**601.706740**

Step - 3: Lower limit = -**9394.69**

Upper limit = -**8903.31**

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