Multiple choice

There are 100 students in 3 sections A, B and C of a class. The average marks of all the 3 sections was 84. The average of B and C was 87.5 and the average marks of A is 70. The number of students in A was-

  1. 30

  2. 35

  3. 20

  4. 25
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C Correct answer
Explanation

Let students in A = x, then students in B + C = 100 - x. Total marks = 100 × 84 = 8400. Section A marks = 70x. Combined marks of B and C = 87.5(100 - x) = 8750 - 87.5x. So: 70x + (8750 - 87.5x) = 8400. Solving: -17.5x = -350, so x = 20. This is a weighted average problem where section A has lower average than B and C combined.

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