Answer
We are 99% confident that the mean number of books that Americans read either all or part of during the year 1978 is between 17.19 and 20.41.
Work Step by Step
Here we have n = 1006, df = n-1 = 1005, x̅ = 18.8 and s = 19.8
Confidence = 99%
α = 1 - 0.99 = 0.01, α/2 = 0.005, $t_{α/2} = 2.581$
$E = 2.581 \times \frac{19.8}{\sqrt 1006} = 1.61 $
Lower Bound = x̅ - E = 18.8 - 1.61 = 17.19
Upper Bound = x̅ + E = 18.8 + 1.61 = 20.41
