In a class of 60 students there are 30 girls. The average weight of these girls is 58 Kg and average weight of the full class is 63 kgs. What is the average weight of the boys of the class?
Total number of students = 60 and number of girls = 30
=> Number of boys in class = 60 - 30 = 30
Average weight of girls = 58 kg
=> Total weight of girls = $$58 \times 30 = 1740$$ kg
Similarly, total weight of full class = $$63 \times 60 = 3780$$ kg
=> Total weight of boys = 3780 - 1740 = 2040 kg
$$\therefore$$ Average weight of boys = $$\frac{2040}{30} = 68$$ kg
=> Ans - C)
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