Question 921163
sum of scores of all boys  = no of boys * mean score of boys 
                            = 38*71
                            =2698
sum of scores of all girls  = no of girls * mean score of girls 
                            = 22*78
                            =1716
total   =2698+1716 =4414
mean = total / total no of boys girls 
       =4414/(22+38)
       =4414/60
       =73.567
mean score of entire class  = 73.567