Square root P

Example: Breast Cancer Power Suppose we wish to test the hypothesis that women with a sister who had breast cancer are at higher risk for Breast cancer themselves. Assume prevalence among 5054 year old women is 2%, but we have reason to believe that those with sisters who had breast cancer is 5%. if we interview 500 women with a sister who had breast cancer, what is our power to detect this difference using a two sided test with significance level oc = 0.05? l