#33 How Many Handshakes?

1.) 45 is the answer for the first one, for there being 10 students in the class.

2.) For the second one, the answer is 55. Adding one person adds 10 more handshakes, because he needs to shake all 10 of the other students’ hands.

3.) For 20 students, it’s 190. I used the pattern (adding 19 + 18+....+1).