It's just a matter of averaging the two percentages. But that doesn't explain why. Assume that there are N men and N women in the population. That means there are 2N men and women total in the population. Then 25% of N or 0.25N and married men and 30% of N or 0.3N are married women. That's a total of 0.25N+0.3N or 0.55N married people. Now the question is : 0.55N is what percent of 2N? IS/OF = 0.55N/2N = 0.275 = 27.5% That's the same as averaging the two percentages:Edwin