The manufacturer of auto windows discussed in Exercise 18 of Chapter 2 has developed a new plastic material that can be applied much thinner than the conventional material. To use this material, however, the production machinery must be adjusted. A trial adjustment was made on one of the 10 machines used in production, and a sample of 25 windshields measured. This sample had a mean thickness of 2.9 mm. Using the standard deviation of 0.25 mm, does this adjustment provide for a smaller thickness in the material than the old adjustment (4 mm)? (Use a hypothesis test and level of significance of 0.01.

Assume the distribution of thickness is approximately normal.)

 LO.1