Answers

2016-02-22T12:32:23+05:30
 The mean weight of 60 students = 40 kg
ie     The sum of 60 student weight
         ----------------------------------------   = 40
                              60
              sum of the 60 student           = 40 * 60   = 2400 kg
   the weight of (boys + girls)               = 2400
                            
any one information ie either boys or girls number then only we can solve this sum

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