Green flag to start 8 people stand in a circle and shake hands with each other. How many handshakes are there? n*(n-1)/2 Remember - A person cannot shake their own hand so n people, in this case, 8 people will shake hands with n-1 people, in this case 7 people. Also, the two same people shaking hands is counted only once.
If n = 8, n*(n-1)/2 (8*7) /2 = 28 Another way of thinking about it is Person #8 shakes 7 other hands, #7 shakes 6 other hands, #6 shakes 5 other hands, ... person #1 shakes no hands 7 + 6 + 5 + 4 + 3 + 2 + 1 = 28
