#33 How Many Handshakes

1)There were 45 handshakes because if there were 10 students then you start adding the numbers 9 to 1.
2)There were 55 handshakes because if there were 11 students then you start adding the numbers 10 to 1.
3)There were 190 handshakes because if there were 20 students then you start adding the number 19 to 1.