Multiple choice

In a class of 100 students, the average weight is 30 kg. If the average weight of the girls is 24 kg and that of the boys is 32 kg, then what is the number of girls in the class?

  1. 25

  2. 26

  3. 27

  4. 28
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A Correct answer
Explanation

Let G be the number of girls and B be the number of boys. G + B = 100. The total weight is 24G + 32B = 30 * 100 = 3000. Substituting B = 100 - G, we get 24G + 3200 - 32G = 3000, so 8G = 200, G = 25.

AI explanation

Using the method of alligation, the ratio of the number of girls to boys is (32 - 30) : (30 - 24), which is 2 : 6 or 1 : 3. Since the total number of students is 100, the number of girls is (1 / (1 + 3)) times 100, equaling 25. The number of girls is 25.

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