A recent poll of 85 randomly selected cable subscribers found that 39% would be willing to pay extra for a new nature channel.

For a 95% confidence interval for a population proportion, use the estimate plus or minus about two standard errors. Here, the estimate is 0.39 and the standard error is √(0.39 × 0.61 ÷ 85) ≈ 0.053, so the interval is about 0.39 ± 0.106, or 28% to 50%. The closest choice is B, between 29% and 49%.

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