The average of 7 numbers is 10.8. If the average of the first three be 10.5 and that of the last three is 11.4, find the value of the middle number.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e 9.9.
Total of all 7 numbers = 10.8 × 7 = 75.6
Total of first 3 numbers = 10.5 × 3 = 31.5
Total of last 3 numbers = 11.4 × 3 = 34.2
Middle number = Total - (first 3 + last 3) = 75.6 - (31.5 + 34.2) = 75.6 - 65.7 = 9.9