everyone shakes hands with everyone else in a room . total number of handshakes is 78 . number of persons = ?
in a room of n people , the number of possible handshakes is c ( n , 2 ) or n ( n - 1 ) / 2 so n ( n - 1 ) / 2 = 78 or n ( n - 1 ) = 156 or n = 13 answer is ( a )
divide(divide(multiply(78, const_2), const_3), const_4)