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The average of the numbers of 25 examinations is 18. The average of the numbers of the first 12 examinations is 14 and for the last 12 examinations is 17. What is the number of the 13th exam?

The average of the numbers of 25 examinations is 18. The average of the numbers of the first 12 examinations is 14 and for the last 12 examinations is 17. What is the number of the 13th exam? Correct Answer 78

Given:

The average of 25 examinations = 18

The average of the first 12 examinations = 14

The average of the last 12 examinations = 17

Formula used:

Average = Sum of all observation/Number of observation

Calculation:

Sum of 25 examinations = 25 × 18 = 450

⇒ Sum of the first 12 examinations = 12 × 14 = 168

⇒ Sum of the last 12 examinations = 12 × 17 = 204

⇒ Number in 13th exam = 450 - 168 - 204

⇒ Number in 13th exam = 78

∴ Number in 13th exam is 78.

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