Question

There are seven positive observations. Average of the first four observations is 11 and of the last four observations is 8. If the average of these seven observations is 9, what is the fourth observation?

• A. 13
• B. 18
• C. 17
• D. 15
• E. 23

Answer 1

The correct option is A 13

Total sum of first four observations $=4\times 11=44$
Total sum of last four observation $=4\times 8=32$
Total sum of all observations $=7\times 9=63$
$\therefore$ Fourth observation $=44+32-63$
$=7+-63=13$