1.  The average of 11 numbers is 10.9. If the average of the first six number is 10.5 and that of the last six numbers is 11.4, then the middle number is :
A. 11
B. 11.3
C. 11.4
D. 11.5

Answer: Option D

Explanation:

Middle number
=[(10.5 x 6 + 11.4 x 6) - 10.9 x 11]
= (131.4 - 119.9)
= 11.5