Depending on what university, your chances may already be limited because you are a Jr., and those sororities who are participating in Informal MAY be your best shot at getting a bid.
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Facile remedium est ubertati; sterilia nullo labore vincuntur. I think pearls are lovely, especially when you need something to clutch. ~ AzTheta
The Real World Can't Hear You ~ GC Troll
OK. There is quota (the maximum amount of new members you can get through formal recruitment) and total (the maximum number of members a group can have). A group may do informal if they did not meet quota OR if they are still below total. They are not required to do informal, however. A chapter that has just one open spot may have a friend of the chapter already in mind, for example, and may offer her membership without holding rush.