Chapter 9 - Section 9.2 - Assess Your Understanding - Applying the Concepts - Page 449: 34

We are 90% confident that the mean tensile strength of the resin cement is between 228.31 N and 256.09 N.

Here we have n = 72, df = n-1 = 71, x̅ = 242.2 and s = 70.6 Confidence = 90% α = 1 - 0.90 = 0.10, α/2 = 0.05, $t_{α/2} = 1.67$ $E = 1.67 \times \frac{70.6}{\sqrt 72} = 13.89 $ Lower Bound = x̅ - E = 242.2 - 13.89 = 228.31 Upper Bound = x̅ + E = 242.2 + 13.89 = 256.09