population proportion

Question

Assume that a sample is used to estimate a population proportion p. Find the 98% confidence interval for a sample of size 313 with 69% 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

CI = sample proportion (phat) +/- z-critical * sqrt(phat*(1-phat)/sample size))

phat = 0.69, the proportion of successes in probability form (between 0 and 1)

sample size = 313

z-critical for 98%: CI is middle 98% of area under normal curve and thus there is 1% on each end, so z-critical is probability from standard normal probability table associated with 99%.