The average age of 30 students in a class is 14 years. When the teacher's age is included, the average becomes 15 years. What is the teacher's age?

हल

1. 01

   The 30 students together account for $30 \times 14 = 420$ years.

2. 02

   With the teacher there are 31 people averaging 15, so the new total is $31 \times 15 = 465$ years.

3. 03

   The teacher's age is the difference: $465 - 420 = 45$ years.