Assume that a sample is used to estimate a population proportion p. Find the 98% confidence interval for a sample of size 280 with 126 successes

Question

Assume that a sample is used to estimate a population proportion p. Find the 98% confidence interval for a sample of size 280 with 126 successes. Enter your answer as an open-interval (i.e., parentheses) using decimals (not percents) accurate to three decimal places.

98% C.I. = 

Answer should be obtained without any preliminary rounding. However, the critical value may be rounded to 3 decimal places.

Answer 1

compute sample proportion phat = 126/180

n = 280

z-critical = 2.33

CI = phat +/- z-critical * sqrt(phat*(1-phat)/n)