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The mean weight of 150 students in a class is 60 kg. The mean weight of boys is 70 kg and that of girls…

Let the number of boys be \(b\) and girls be \(150 - b\). Then \(70b + 55(150 - b) = 150 \times 60 \implies 15b + 8250 = 9000 \implies 15b = 750 \implies b = 50\).

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The mean weight of 150 students in a class is 60 kg. The mean weight of boys is 70 kg and that of girls is 55 kg. What is the number of boys in the class?

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Correct answer A

Let the number of boys be bb and girls be 150−b150 - b. Then 70b+55(150−b)=150×60  ⟹  15b+8250=9000  ⟹  15b=750  ⟹  b=5070b + 55(150 - b) = 150 \times 60 \implies 15b + 8250 = 9000 \implies 15b = 750 \implies b = 50.

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