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Continuing the Field Poll example, p' = 0.79 from 400 of 506 surveyed. For a 90% confidence level, z(0.05)=1.645. What is the approximate error bound, EBP?
A0.790
B1.645
C0.030
D0.500
Answer & Solution
Correct answer: C. 0.030
1. EBP = z*sqrt(p'q'/n) with p' ≈ 0.7905, q' ≈ 0.2095, n = 506.
2. EBP = 1.645*sqrt((0.7905)(0.2095)/506) ≈ 1.645*0.01809.
3. That product is approximately 0.030.
4. Option A repeats the point estimate itself rather than computing a margin of error around it.
_Source: OpenStax Introductory Statistics (CC BY 4.0), Ch 8 "Confidence Intervals", section 8.3 A Population Proportion_
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