Multiple choice

The average age of 25 students in a class is 12 years. If three students aged 11, 12 and 13 respectively left the class, what would be the change in the average age of the students in the class?

  1. $+ 2$
  2. $- 1$
  3. $0$
  4. $+ 1$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total age of 25 students = 25 × 12 = 300 years. The three leaving students have ages 11, 12, 13 (sum = 36). New total = 300 - 36 = 264. New count = 25 - 3 = 22. New average = 264/22 = 12 years. Change = 12 - 12 = 0. The three students' average (36/3 = 12) equals the class average, so no change.

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