Multiple choice

The average of the students of a class is 12 years. The average age of 15 of them 10 years and the average age of the remaining is 13 years. How many students there in the class?

  1. 35

  2. 40

  3. 45

  4. 50

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If there are n students, the total age is 12n. The 15 students contribute 15 x 10 = 150 years, and the remaining n - 15 contribute 13(n - 15) years. Solving 12n = 150 + 13(n - 15) gives n = 45.