Please explain

Question

How did you get the answer square root (0.28)(0.72)/427

Answer 1

Step 1:

Definition of specific confidence interval for a proportion : .

where is the population proportion.

is the sample proportion = 28 % of women who purchase books online.

n is the sample size = 427 women.

is the confidence interval.

For 95% of confidence interval, .

Step 2:

Substitute and in the above formula.

This is how we get .

Conclusion:

95% of confidence interval for the proportion of all 29 % women purchase books online is .