Question

The AP reported that in a sample of 507 people only 142 correctly described the Bill of Rights as the first ten amendments to the U.S. Constitution. Calculate a 95% confidence interval for the proportion of the entire population that could give a correct description.

Answer 1

CI95 = p ± (1.96)[√(pq/n)]
...where p = x/n, q = 1 - p, and n = sample size.
Note: ± 1.96 represents 95% confidence interval.

For p in your problem: 142/507 = .28
For q: 1 - p = 1 - .28 = .72
n = 507

Hopefully, you can take it from here.