The average weight of 40 students in a class is 55 kg. Six students of them whose average weight is 52 kg leave the class and another group of 6 students whose average weight is 42 kg joins the class. What is the new average of the class ? (in kg)
Total weight of original 40 students = $$40 \times 55 = 2200$$ kg
Weight of 6 students who left = $$6 \times 52 = 312$$ kg
Weight of 6 new students who joined = $$6 \times 42 = 252$$ kg
=> New weight of new group of 40 students = $$(2200 - 312 + 252)$$ kg
= $$2140$$ kg
$$\therefore$$ Required Average = $$\frac{2140}{40}$$
= $$53.5$$ kg
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