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    Question

    The average weight of 100 students in a class is 46 kg.

    The average weights of boys and girls are 50 kg and 40 kg respectively. What is the difference between the number of boys and girls?
    A 30 Correct Answer Incorrect Answer
    B 25 Correct Answer Incorrect Answer
    C 20 Correct Answer Incorrect Answer
    D 10 Correct Answer Incorrect Answer

    Solution

    Let the number of boys and girls be x and (100 - x) respectively. According to the question,  Mean = {50x + 40(100 - x)}/100 ⇒ 46 = {50x + 40(100 - x)}/100 ⇒ 4600 = 50x + 4000 - 40x ⇒ 4600 - 4000 = 10x ⇒ x = 600/10 ⇒ x = 60 So, the number of boys is 60. Number of girls = 100 – x = 40 Required difference = 60 – 40 = 20

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