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The average of 25 results is 18; that of first twelve is 14 and of last twelve is 17. Find the thirteenth result.
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- 68
- 78
- 79
- 87
- 68
Correct Option: B
The average of 25 results =18;
Sum of 25 results = Average × their number
Sum of 25 results = 18 × 25 = 450
The average of first twelve = 14
Similarly, Sum of 1st twelve results = 12 × 14 = 168
and The average of last twelve = 17
and sum of last twelve results = 12 × 17 = 204
∴ Thirteenth result = 450 – 168 – 204 = 78
