Question

In a class of 20 students, how many conversations must be had so that every student talks to every other students in the class?

Answer 1

190

Explanation:

Similar to the handshake problem, if every student must talk with another person, each student will talk to 19 other students. However, a conversation consists of two people, so we must divide the number of ways we can rearrange the two people. Therefore, our answer is 190