Preliminary and Confidence Interval

Question

If  and , construct a 95% confidence interval about the population proportion. Round your answers to three decimal places.

Preliminary:

1. Is it safe to assume that  of all subjects in the population?
2. Verify  Round your answer to one decimal place. 

Confidence Interval: What is the 95% confidence interval to estimate the population proportion? Round your answer to three decimal places.

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Answer 1

We are not given information about the population for which we are constructing the confidence interval, so we can't know whether the sample size is less than 5% of the population size.

np = 24 and n(1-p) = 96, so can assume normal distribution

CI = phat +/- z-critical * sqrt(phat * (1-phat)/n) = 0.2 +/- 1.96 * sqrt(0.2 * 0.8/120)

Leave it to you to complete the computation of the confidence interval