Multiple choice

The average age of a class was 15 years.When 5 boys whose average age was 12 years and 6 months were admitted in the class, the average was reduced to 6 months.How many students were there in the class originally?

  1. 20

  2. 24

  3. 25

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

Let n be the original number of students. Total age = 15n. 5 new boys add 5 × 12.5 = 62.5 years. New average = (15n + 62.5)/(n+5) = 14.5. Solving: 15n + 62.5 = 14.5n + 72.5, so 0.5n = 10, giving n = 20 students.

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