ANN ARBOR. Mich.--The University of Michigan this week unveiled a new formula for determining which students may take limited enrollment courses in mechanical engineering: Divide each student's grade point average (GPA) by four, multiply by one-sixteenth of his total credit hours, multiply again by the number of terms he has studied at the university, raise to the .585 power, add the student's total number of credit hours divided by 96. subtract one, and multiply by 1000.

This yields the student's "priority index" number. The students with the highest numbers will have first dibs on six popular engineering courses.

A Necessary Formula

David Pratt, chairman of Michigan's department of mechanical engineering and applied mechanics, said this week the complicated formula is necessary because the department wanted to take into account many factors--including GPA, class standing, and credit hours--when choosing among students.