You can choose from 20 students for the first student, 19 for the second, 18 for the third, ..., 14 for the seventh student.
That gives you 20 * 19 * 18 * 17 * 16 * 15 * 14.
That number would allow you to write the students in different order. Since order here does not matter, any group with the same students in any order is the same group, you need to divide by the number of way you can order 7 items. Divide by 7 * 6 * 5 * 4 * 3 * 2 * 1
(20 * 19 * 18 * 17 * 16 * 15 * 14)/(7 * 6 * 5 * 4 * 3 * 2 * 1) = 77,520
Answer: 77,520
