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 5

C 42

D 36

Solution

Correct Answer: Option A

Numbers of students in section A = x 
∴ Numbers of students in section B and C = (100 – x) 
∴ x 70 + (100 – x) 87.5 = 84 100 
=> 70x + 87.5 100 – 87.5x = 8400 
=> 8750 – 17.5x = 8400 
=> 17.5x = 8750 – 8400 => x = 20.

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