Multiple choice

The average weight of A, B and C is 72 kg. If the average weight of A and B is 78 kg and the average weight of A and C is 71 kg, then what is the weight of A? (in kg)

  1. 83

  2. 82

  3. 81

  4. 80
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A+B+C = 72*3 = 216. A+B = 78*2 = 156. A+C = 71*2 = 142. (A+B) + (A+C) = 156 + 142 = 298. 2A + B + C = 298. Subtract (A+B+C=216) from (2A+B+C=298) to get A = 82.

AI explanation

Using the basic average formula, the total weight of A, B, and C is 3 times 72, which equals 216 kg. The total weight of A and B is 2 times 78, equaling 156 kg, and the total weight of A and C is 2 times 71, equaling 142 kg. Adding the weights of A and B to the weights of A and C gives 298 kg, which includes A's weight twice along with the weights of B and C. Subtracting the combined weight of A, B, and C, which is 216 kg, from this total leaves exactly twice the weight of A: 298 minus 216 is 82 kg, so A weighs 82 kg.

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