The average age of 19 boys in a class is 21 years. If the teacher's age is included, the average increases to 22 years. What is the teacher's age?

The average age of 19 boys in a class = 21 years
Sum total of ages of 19 boys = 19 × 21 years = 399 years
The average age of 19 boys and teacher in a class = 21 years
Sum total of ages of 19 boys and teacher = 20 × 22 years = 440 years
∴ Age of teacher = Sum total of ages of 19 boys and teacher - Sum total of ages of 19 boys
Age of teacher = ( 440 – 399 ) years = 41 years