It's there if you want it, but only something like 10% of students actually participate. That being said, there are enough frats that there's always one throwing a party. Because Greeks are generally so active at campus it might seem more prevalent than only 10%. There are both on-campus and off-campus fraternity houses, but sororities have to have their official housing in dorms buildings rather than their own housing structures. I have heard rumor that this is due to some really weird and ancient law in Pittsburgh that anything more than 3 or 4 women living together is technically considered a brothel, and that's why they have to be in dorms. (I can't verify if that's true or not, but it certainly makes for a good story)
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