Exercise 10-28 presented measurements of plastic coating thickness at two different application temperatures. Test H₀: σ²₁ = σ²₂ against H₁ : σ²₁ ≠ σ²₂ using α = 0.01.

Exercise 10-28

The thickness of a plastic film (in mils) on a substrate material is thought to be influenced by the temperature at which the coating is applied. In completely randomized experiment, 11 substrates are coated at 125°F, resulting in a sample mean coating thickness of x̅₁ = 103.5 and a sample standard deviation of s₁ = 10.2. Another 13 substrates are coated at 150°F for which x̅₂ = 99.7 and s₂ = 20.1 are observed. It was originally suspected that raising the process temperature would reduce mean coating thickness.