We are asked to determine the sample size to determine the difference in the proportion of men and women who own smartphones with a confidence of 99% and an error of no more than 0.03. If we assume that both samples are equal then we can use the following formula:
Where Z is the confidence and E is the error. Replacing the values we get:
Solving the operations we get:
Therefore, each sample of men and women should be of 545.