There are 100 students in 3 sections A, B and C of a class. The average marks of all the three sections was 84. The average of B and C was 87.5 and the average marks of students in A section was :

There are 100 students in 3 sections A, B and C of a class. The average marks of all the three sections was 84. The average of B and C was 87.5 and the average marks of students in A section was :
[A]20
[B]25
[C]30
[D]35

20
Numbers of students in section A = x
∴ Numbers of students in section B and C = (100 – x)
∴ x \times 70 + (100 – x) \times 87.5 = 84 \times 100
=> 70x + 87.5 \times 100 – 87.5x = 8400
=> 8750 – 17.5x = 8400
=> 17.5x = 8750 – 8400
=> x = \frac{350}{17.5} = 20
Hence option [A] is correct answer.

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