At the end of a banquet 10 people shake hands with each other . How many handshakes will be in total?
A
100
B
20
C
45
D
90
Correct Answer: 45
Everybody does 9 handshakes - but then they are counted twice, so 10 * 9 /2 = 45. Alternative calculation: Person no 1 does 9 handshakes Person no 2 does 8 - he already has shaken hands with no1 And so on … person no 9 does 1 handshake with person no 10 Btw person no10 has already shaken everybody’s hand, ok So we get 9 + 8 + … + 1 The seven years old Gauß might tell you that this is 10 * 9 / 2 = 45