Question: The average of thirteen numbers is 9. The average of first six numbers is 5 and the average of last six numbers is 7. What is the middle number?
Options:
(A) 47
(B) 45
(C) 25
(D) 37
(E) 44 Random thoughts:
The total of thirteen numbers = 13X9 = 117
The total of first 6 and last 6 numbers is = 6 X 5+6 X 7 = 72
So, the middle number is (117 - 72 ) = 45 The final answer: (B).