The TOO Sorority has a tough pledging program-it requires its pledges to master the Greek alphabet forward, backward, and "sideways." During the last pledge period, two- thirds of the pledges failed to learn it backward and three quarters of them failed to learn it sideways; 15 of the 36 pledges failed to master it either backward or sideways. Because admission into the sisterhood requires both backward and sideways mastery, what fraction of the pledges were disqualified on this basis? 0