The average age of a group of 35 students is 15 years. If a teacher is included in the group, then the average age increases by 2 months. The age of the teacher (in years) is

21

Average age of 35 students only = 15 years

Average age of 35 students + 1 class teacher = 15 years 2 months

We know that,

Average = (Total sum)/(Total numbers)

Total age of 35 students only = 35 × 15 = 525

Total age of 35 students and the class teacher = 36 × 15.16 = 546

Age of teacher = 546 - 525 = 21 years