Question

The average age of 57 students of a class is 13 years. If the age of the teacher is also included, the average age of the whole group becomes 14 years. The age (in years) of the teacher is:

• A. 70
• B. 69
• C. 72
• D. 71

Answer 1

Answer:

D. 71

Average of 57 students = 13 years
$\text{Total age of students} = 57 \times 13 = 741$

Including the teacher: total people = 58, average = 14

$\text{Total age (including teacher)} = 58 \times 14 = 812$

Teacher’s age:

$812 - 741 = 71$