Multiple choice

The average marks of 50 students in a class is 72. The average marks of boys and girls in that subject are 70 and 75 respectively. The number of boys in the class is –

  1. 20

  2. 35

  3. 25

  4. 30
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let boys = b. Total marks = 50 × 72 = 3600. Boys' marks = 70b, girls' marks = 75(50-b). 70b + 3750 - 75b = 3600, so 5b = 150 and b = 30. Options 20, 25, 35 don't satisfy the weighted average equation.

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