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 ? एक कक्षा के तीन सेक्शनों A, B और C में 100 छात्र हैं। तीनों सेक्शनों के औसत अंक 84 हैं। B और C का औसत 87.5 और A के औसत अंक 70 थे। । A में छात्रों की संख्या कितनी थी?

  1. 15

  2. 25

  3. 30

  4. 20
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D Correct answer
Explanation

Let students in A = a, B = b, C = c. Total: a + b + c = 100. Overall avg 84, so total marks = 8400. Avg of A = 70, so marks in A = 70a. Avg of B and C = 87.5, so marks in B + C = 87.5(b + c). Also 70a + 87.5(b + c) = 8400. Substituting b + c = 100 - a: 70a + 87.5(100 - a) = 8400. Solving: -17.5a + 8750 = 8400, giving a = 20.

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