What is the average of first 21 multiples of 7 ?
Select
A) 67
B) 69
C) 77
D) 79
E) 81
Required average = 7(1+2+....+21) / 21   (7/21)X ( (21x22) / 2 ) (because sum of first 21 natural numbers)   = 77   77
<result>C</result>
What is the average of first 21 multiples of 7 ?