Multiple choice

The average of 21 results is 54. If the average of the first 11 results is 51 and that of the last 11 is 57, find the 11th result.

  1. 48

  2. 50

  3. 54

  4. 56
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C Correct answer
Explanation

The sum of 21 results is 21 * 54 = 1134. The sum of the first 11 is 11 * 51 = 561, and the sum of the last 11 is 11 * 57 = 627. The 11th result is counted twice, so it is (561 + 627) - 1134 = 1188 - 1134 = 54.

AI explanation

The total sum of all 21 results is 21 times 54, which equals 1134. The sum of the first 11 results is 11 times 51, equaling 561, and the sum of the last 11 results is 11 times 57, equaling 627. Adding these two sums gives a combined total of 1188. Because the 11th result is counted twice in the sum of 1188, you subtract the overall sum of 1134 from 1188 to find the 11th result of 54.

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