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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,Β  Mean = {50x + 40(100 - x)}/100 β‡’ 46 = {50x + 40(100 - x)}/100 β‡’ 4600 = 50x + 4000 - 40x β‡’ 4600 - 4000 = 10x β‡’ x = 600/10 β‡’ x = 60 So, the number of boys is 60. Number of girls = 100 – x = 40 Required difference = 60 – 40 = 20

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