Question

The average of 17 numbers is 10.9. If the average of first nine numbers is 10.5 and that of the last 9 numbers is 11.4, the middle number is:

• A. 11.8
• B. 11.4
• C. 10.9
• D. 11.7
• E. None of these

Answer 1

The correct option is A 11.8

Sum of first nine numbers + sum of last nine numbers
$=10.5\times 9+11.4\times 9=21.9\times 9=197.1$
Hence, the middle number
$=197.1-17\times 10.9$
$=197.1-185.3=11.8$