The sum of age of 40 students = 12 × 40 = 480 The sum of age of 41 people = 13 × 41 = 533 ⇒ Difference = 533 - 480 = 53 years Retirement age = 55 years ∴ The retirement age of the teacher is 55 years, then he will retire after 2 years(55 - 53). The correct option is 2 i.e. 2 years