Let's consider first what equation we must use:
⇒ use Combination Formula ⇒
⇒ where 'n' is the total number of items and 'r'
is the number of items to choose
Let's look at the problem:
- total number of students: 18
- number of students needed for debate: 4
Let's plug it in:
Thus there are 3060 ways
Answer: 3060 ways
Hope that helps!