Multiple choice

The average of 20 boys and their teacher is 10 years. When the teacher's age is excluded, the average age decreases by 2 years. What is the age of the teacher?

  1. 40 yr.

  2. 50 yr.

  3. 60 yr.

  4. 70 yr.

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

Total age of 20 boys + teacher = 21 × 10 = 210 years. Average of 20 boys alone = 10 - 2 = 8 years. Total age of 20 boys = 20 × 8 = 160 years. Teacher's age = 210 - 160 = 50 years.