Chapter 9 - Section 9.2 - Assess Your Understanding - Applying the Concepts - Page 449: 29c

We are 90% confident that the mean BAC in fatal crashes in which the driver had a positive BAC is between 0.1647 and 0.1693 g/dL.

Here we have n = 51, df = n-1 = 50, x̅ = 0.167 and s = 0.010 Confidence = 90% α = 1 - 0.90 = 0.10, α/2 = 0.05, $t_{α/2} = 1.676$ $E = 1.676 \times \frac{0.010}{\sqrt 51} = 0.002 $ Lower Bound = x̅ - E = 0.167 - 0.002 = 0.1647 Upper Bound = x̅ + E = 0.167 + 0.002 = 0.1693