When dealing with confidence intervals for proportions, the formula is

p^ +/- Zcritical(standard deviation)

Where p^ = r/n,  r is the number of observations and n is the sample size

For a 95% confidence interval, Zcritical = 1.96

The standard deviation is square root[(p^)(1 - p^)/n]

The margin of error, denoted at E = Zcritical(standard deviation)