Multiple choice

The total number of students in sections A and B of a class is 72. The ratio of the number of students in A and B is 7 : 5. The average weight (in kg) of the students in section B is 20% more than that of the students in section A. If the average weight of all the students in the class is 52 kg, then what is the average weight (in kg) of the students in section B?

  1. 58.2

  2. 57.9

  3. 57.6

  4. 56.4
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C Correct answer
Explanation

Ratio A:B = 7:5. Students in A = 42, B = 30. Let avg weight of A = x, then B = 1.2x. Total weight = 42x + 30(1.2x) = 72 * 52. 42x + 36x = 3744. 78x = 3744, x = 48. Avg weight of B = 1.2 * 48 = 57.6.

AI explanation

Using the ratio 7:5 for the 72 students, section A has 42 students and section B has 30 students. Let the average weight of section A be x, so section B's average is 1.2x. The total weight equation is 42(x) + 30(1.2x) = 72(52), which simplifies to 42x + 36x = 3744, meaning 78x = 3744. Solving for x gives section A's average as 48, and multiplying by 1.2 gives section B's average of 57.6.

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