Mathematics: Combinations and Counting

Question

A high school graduating class has 400 members. The principal must select 3 of these students to attend the annual state student conference. How many ways can this be done?

Answer 1

again, order is not important: A,B,C is considered the same selection and C,B,A

40 choose 3 = 40*39*38 / 6 = 20*39*38/3 = 20*13*38 = 760*13 = 9880