As far as I know, they do not use the quota system at IUB. Each chapter determines how many PNMs they wish to take and as long as it doesn't put them over chapter total. So, some chapters may take 12 and others may take 50, it all depends.
From
http://www.indiana.edu/~gogreek/faq/:
Quota
The number of women in which each sorority may pledge during the formal recruitment process. (IU sororities base their quota on house capacity and the number of women going abroad or living out of the chapter house. Panhellenic does not set one quota for all 19 chapters.)