Question

there are 21 students in a chemistry class. the students must pair up to work as lab partners, but, of course, one student will be left over to work alone. in how many ways can the students be paired up?

Answer 1

3800 ways.

Explanation:

One of 21 students will be working alone.

Out of the other 20 There are 20C2 ways that the students can pair up

Which is 20*19 / 2*1

= 190 ways.

So, for 21 students the number of ways

= 190 * 21

= 3800.