Multiple choice

The average of $15$ results is $50$. If the average of first $8$ results is $48$ and that of the last $8$ is $53$, find the eigth result.

  1. $95$
  2. $80$
  3. $71$
  4. $58$
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D Correct answer
Explanation

Total of 15 results = 15 * 50 = 750. Sum of first 8 = 8 * 48 = 384. Sum of last 8 = 8 * 53 = 424. The 8th result is counted twice. (384 + 424) - 750 = 808 - 750 = 58.

AI explanation

Using the basic average formula, the total sum of all 15 results is 15 times 50, which is 750. The sum of the first 8 results is 8 times 48, giving 384, and the sum of the last 8 results is 8 times 53, giving 424. Because the 8th result is counted in both of these smaller sums, adding them gives 808, which counts the 8th result twice; therefore, the 8th result is 808 - 750 = 58. The result is 58.

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