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The average of 15 numbers is 7. If the average of the first 8 numbers is 6.5 and the average of the last 8 numbers is 8.5, then the middle number is :
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- 10
- 23
- 13
- 15
- 10
Correct Option: D
Given that , The average of 15 numbers = 7
The average of the first 8 numbers = 6.5
and the average of the last 8 numbers = 8.5
Middle i.e. eighth number = 8 × 6.5 + 8 × 8.5 – 15 × 7
Middle i.e. eighth number = 52 + 68 – 105
Middle i.e. eighth number = 120 – 105 = 15
