Multiple choice

The average weight of 3 boys is 72 kg. If the first boy is 7 kg heavier than the second and the weight of the second boy is 5 kg more than that of the third, then the approximate weight of the first boy is

  1. 74 kg

  2. 70 kg

  3. 75 kg

  4. 78 kg

  5. 60 kg
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D Correct answer
Explanation

Let the third boy's weight be x. The second boy is x + 5, and the first boy is (x + 5) + 7 = x + 12. The average weight is (x + 12 + x + 5 + x) / 3 = 72, which simplifies to 3x + 17 = 216, so 3x = 199 and x = 66.33. The first boy's weight is 66.33 + 12 = 78.33 kg, which is approximately 78 kg.

AI explanation

The total weight of the three boys is 3 times 72, which equals 216 kg. Let the third boy's weight be x; then the second boy weighs x + 5, and the first boy weighs (x + 5) + 7, which is x + 12. The equation is x + x + 5 + x + 12 = 216, simplifying to 3x + 17 = 216. Solving for x gives 3x = 199, so x is approximately 66.3. The first boy's weight is approximately 66.3 + 12, which is 78.3 kg, making the closest approximate weight 78 kg.

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