Question

In a conference, seven people shake hands with
each other once. How many handshakes will there
be altogether?
(1) 14 (2) 20
(3) 21 (4) 25

Answer 1

6+5+4+3+2+1+0=21
every person shakes hands with 6 members
since one is already counted with the previous member, it has to be added as such.