There is a little bit of logic involved here. It says the ratio of male to female students is 2 to 3. You add 400 male students, and now the ratio is 1 to 1. Well, if you're increasing it 400, you're adding a third of the students if you're getting it to a 1 to 1 ratio, aren't you? Well, if the ratio is now 1 to 1 and you've added 400 students, and 400 students comprise a third of the student body, that tells us that there are 1200 females and there are 1200 males. So, the answer to the total number would be 2400.