Question

How many combinations of 4 students can a teacher choose from 30 students?

a. 27,405

b. 657,720

c. 120

d.810,000

Answer 1

A

Explanation:

27,405

Answer 2

b. 27,405

Explanation:

So, we have a total population of 30 (n) and we sample 4 (r) from it.

Now, is it a combination or a permutation? Does the order matter? Is it important that the teacher picked John before Andrew? No. So, it's a combination:

C(n,r)=C(30,4)

`C(30,4) = (30!)/(4| (30-4)!) = 27405`

So, the teacher has 27,405 ways to combine groups of 4 students from his 30-student class.