Multiple choice

In a school with 600 students, the average age of the boys is 12 years and that of the girls is 11 years. If the average age of the school is 11 years 9 months, then the number of boys in the school is

  1. 150

  2. 250

  3. 350

  4. 450
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let x boys, y girls. x + y = 600. Average age = 11 years 9 months = 11.75 years. So (12x + 11y) / 600 = 11.75. Substituting y = 600 - x: 12x + 11(600 - x) = 7050, so x + 6600 = 7050, x = 450 boys. Option D is correct.

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