The average age of a class of 19 students is 20 years. The average increased by 1 when the teacher's age also included. What is the age of the teacher?	Choices: A) 39 B) 41 C) 40 D) 42 E) 43

Rationale: total age of all students = 19 ã — 20 total age of all students + age of the teacher = 20 ã — 21 age of the teacher = 20 ã — 21 â ˆ ’ 20 ã — 19 = 20 ( 21 â ˆ ’ 19 ) = 20 ã — 2 = 40 answer is c .
Answer: C