The average of 25 numbers is 18. The average of the first 12 of these numbers is 14 and that of the last 12 of these numbers is 17. The 13th number is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is Option 2 i.e. 78.
We know that,
Average = Sum of observations/Number of observations
Let the 13th result be x
Total of 25 results = 25 × 18 = 450
Total of first 12 result = 12 × 14 = 168
Total of last 12 result = 12 × 17 = 204
According to the question
⇒ 450 = 168 + 204 + x
⇒ x = 78