Multiple choice

The average age of 30 boys in a class is 10 years. If the age of their teacher is also included, the average age increases by one year. What is the teacher's age?

  1. 38

  2. 30

  3. 40

  4. 41
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The total age of 30 boys is 30 × 10 = 300 years. After including the teacher, there are 31 people with an average age of 11 years, so the total becomes 31 × 11 = 341 years. The teacher's age is 341 - 300 = 41 years. This is solved by understanding that the total sum of ages increases when a new person is added.

Keep practicing — related questions