Q1. The average age of a class of 40 students and a teacher is reduced by 0.5 years if the teacher is excluded. If the initial average age is 18 years, what is the age of the teacher?
A 38 years Correct
B 40 years
C 39 years
D 41 years
Explanation
Initially there are 41 people: 40 students and one teacher. Their average age is 18 years, so the total age is 41 × 18 = 738 years. When the teacher is excluded, the average falls by 0.5 years, becoming 17.5 years for 40 students. The students’ total age is 40 × 17.5 = 700 years. The teacher’s age is therefore 738 - 700 = 38 years. The ages 39, 40, and 41 do not match these totals.