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

a. 27,405

b. 657,720

c. 120

d.810,000

b.  27,405

Step-by-step 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)

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

according to the triangle sum theorem, all the angles in a triangle must add up to 180 degrees. if we know one angle is already 90, we do 180-90=90. the other 2 angles must add up to 90, exactly.

step-by-step explanation: