The average age of a class of 20 students is 21 years. The average increased by 1 when the teacher's age also included. What is the age of the teacher?  Choose the correct answer:
A) 40	B) 41	C) 42	D) 45	E) 43

Rationale: "total age of all students = 20 ã — 21 total age of all students + age of the teacher = 21 ã — 22 age of the teacher = 21 ã — 22 â ˆ ’ 21 ã — 20 = 21 ( 22 â ˆ ’ 20 ) = 21 ã — 2 = 42 answer is c ."
Answer: C