Multiple choice

The average of 24 numbers is 68. The average of first 12 numbers is 65.25 and the average of last 11 numbers is 72. Find the 13th number.

  1. 57

  2. 92

  3. 73

  4. 79
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A Correct answer
Explanation

Total sum of 24 numbers = 24 × 68 = 1632. Sum of first 12 = 12 × 65.25 = 783. Sum of last 11 = 11 × 72 = 792. The 13th number = Total sum - (sum of first 12 + sum of last 11) = 1632 - (783 + 792) = 1632 - 1575 = 57.

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