What is the average of first 21 multiples of 4 ?	Choose the correct choice.
A) 44 B) 77 C) 79 D) 81 E) 82

Rationale: "required average = 7 ( 1 + 2 + . . . . + 21 ) / 21 ( 4 / 21 ) x ( ( 21 x 22 ) / 2 ) ( because sum of first 21 natural numbers ) = 44 a"
Answer: A