There are 20 students in a math class. Thirty percent of the students are randomly chosen to participate in a teacher
evaluation. How many combinations of students are possible?

Step-by-step explanation:

20% of 30 is 6 are randomly selected.

30 choose 6 = 30! / (30-6)! 6!

                 = 30! / 24!6!

                 = 30 * 29 * 28 * 27 * 26 * 25

                    <-- 24! cancels

                    6 * 5 * 4 * 3 * 2 * 1

                 = 29 * 28 * 27 * 26 * 25

                  <--- 30 = 6 * 5 cancels

                      4 * 3 * 2 * 1

                = 29 * 7 * 9 * 13 * 25   <--  4 cancels 28, 3 cancels 27, 2 cancels 26

               = 593775

b

step-by-step explanation:

1/4 because there is 4 grades.