19 people (a1, a2,...., a19) are invited to a party. The host and the hostess shake hands with each invitee and also with each other. The invitees shake hands in a circular fashion, i.e. the pairs (a1, a2), (a2, a3), .....,(a18, a19), (a19, a1) shake hands. So, in all there are 58 handshakes. Let S be a set of people such that every pair in S shake hands. The size of S is at most

• hosthostess - 1
  a1a2 -1
  host(a1,a2) -1
  hostess(a1,a2) -1
  Therefore the size of s =(1+1+1+1)=4
• 13 years agoHelpfull: Yes(3) No(2)