Help! I'm not sure how to solve this.

Ms. Lunette has 18 students in her class. She wants to send 3 of these students to pick up books for the class.

How many combinations of 3 students can she choose?

A.
6

B.
54

C.
816

D.
4896

Question

Help! I'm not sure how to solve this.

Ms. Lunette has 18 students in her class. She wants to send 3 of these students to pick up books for the class.
 
How many combinations of 3 students can she choose?
 
 A.
6
 
 B.
54
 
 C.
816
 
 D.
4896

anonymous · Answer

She has 18 and wants to choose 3

mathstudent55 · Answer

This is a problem in which order does not matter.
Let's say the 18 students are named 1 through 18
If she picks 1, 2, 3, that's the same as picking 3, 2, 1.
Once again, order does not matter.

anonymous · Answer

It is hard to visualize, need the formula

anonymous · Answer

ok then. like this? 123. 456. 789. 101112. 131415. 161718.

mathstudent55 · Answer

This is a combination problem (not permutation).

$_nC_r = \dfrac{n!}{r!(n - r)!} $

$_{18}C_3 = \dfrac{18!}{3!(18 - 3)!}$

anonymous · Answer

I am so bad at this. I think it's c

anonymous · Answer

i mean A

mathstudent55 · Answer

How about just doing it together and finding out?

anonymous · Answer

ok

mathstudent55 · Answer

|dw:1401595598244:dw|
Ok so far?