Each student was graded A,B orC.What percent of students are female?

This is an interesting problem, because it plays with your expectations a little bit. My immediate first thought was that the answer would be E. That's because in almost all situations, you'd need to know the percent of students that received a B, versus an A or C. For instance, the answer to this problem would be E:

In a class, each student received a grade A, B or C. What percentage of students in class are females?
1) Of those who received B, 40% were females.
2) Of those who received A or C, 50% were males.

The only reason this one ends up being 'C' is because the two percents are the same - women make up 40% of each group in the class, so they make up 40% of the whole class, regardless of how big the groups are. And the problem disguises that by giving the 60% figure instead of the 40% one in the second statement - I almost didn't notice. Clever trick!