1) not all students whom we have given offers to are going to come. In fact, if on average each student has 3 offers (I think more, as from the GMAT score card, a lot of students are applying to a dozen universities.), only one third of the students in the qq group are going to come. 2) not all the students in the qq group are students with offers. Some are simply gathering in formation. Some are part time, some are previous students. 3) there are two classes, each of 70.  art time plus full time. Together we will have 140 students. The proportion depends on the quality of the applicants. 4) not all students who have paid deposit are going to come. About 1/10 to 1/5 may not come for various reasons.