The critical value used to find a 98% confidence interval is Z = 2.33. n1 = 1400, n2 = 1320 p1 = .5, p2 = .38 q1 = 1 - p1 = .5, q2 = 1 - p2 = .62 To begin, we must find the difference in proportions. This is 0.5 - 0.38 = 0.12. We now use the formula 98 % CI = .12 +/- 2.33*sqrt(((p1*q1)/n1) + ((p2*q2)/n2))) This gives us .12 +/- 2.33*sqrt(((.5*.5)/1400) + ((.38*.62)/1320))) Simplifying, we get .12 +/- .04, so our 98% confidence interval is (0.8, 0.16).