The average age of 30 students is 9 years. If age of their teacher is included, it becomes 10 years. The age of teacher (in years) is

A) 27 years

B) 31 years

C) 35 years

D) 40 years

Correct answer:
D) 40 years

Description for Correct answer:
Age of teacher is (31 X 10 - 30 X 9) = 40 Years


Please provide the error details in above question