The average of 9 numbers is 15. If the average of the first five numbers is 13 and the average of the last five numbers is 17, then what is the fifth number?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 15.
We know that,
Average = Sum of observations/Number of observations
Now,
The average of 9 numbers is 15
The sum of 9 numbers = 9 × 15 = 135
The average of the first five numbers is 13
The sum of first five numbers = 5 × 13 = 65
The average of the last five numbers is 17
The sum of last five numbers = 5 × 17 = 85
Hence, the fifth number = (65 + 85) - 135 = 150 - 135 = 15