Question 189
Consider a group of 15 people. It is possible that each of them knows exactly:
(a) 4 people from the group?
(b) 3 people from the group? (Admit that if $A$ knows $B$ then $B$ knows $A$.)
(a) 4 people from the group?
(b) 3 people from the group? (Admit that if $A$ knows $B$ then $B$ knows $A$.)