In a class of 60 studnets 60% are girls. The average weight of boys is 60kg and that of the girls is 50 kg. What is the average weight (in kg) of the whole class?

54

          60% = \(\frac{3}{5}\)

          Boys   :       Girls

            2      :         3

Average weight of class = \(\frac{(2\;×\;60) + (3\;×\;50)}{5}\)

                                       =  \(\frac{270}{5}\) = 54