Multiple choice

The average weight of a group of 20 boys was calculated to be 89.4 kg and it was later discovered that one weight was misread as 78 kg instead of 87 kg. The correct average weight is

  1. 88.95kg

  2. 89.25kg

  3. 89.55kg

  4. 89.85kg
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Difference in sum = 87 - 78 = 9. Increase in average = 9 / 20 = 0.45. Correct average = 89.4 + 0.45 = 89.85.

AI explanation

The correct weight of 87 kg is 9 kg more than the misread weight of 78 kg, so the total weight increases by 9 kg. Using the average adjustment method, this increase of 9 kg is divided equally among the 20 boys, adding 0.45 kg to the old average. Adding 0.45 kg to 89.4 kg gives the correct average weight of 89.85 kg.

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