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?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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