Answer :
Final answer:
By translating the given conditions into equations and solving those equations, we find that the weight of man A is 75 kg.
Explanation:
The question involves solving a set of equations. The average weight of A, B, and C is 84 kg so the total weight of A, B, and C is 3*84 = 252 kg. When D joins them, the average becomes 80 kg, so the total weight of A, B, C, and D is 4*80 = 320 kg. Therefore, the weight of D is 320 - 252 = 68 kg.
When E (whose weight is 3 kg more than D) replaces A, the average weight of B, C, D, and E is 79 kg. This gives us an equation: (B weight+C weight+D weight+E weight)/4 = 79.
We know that E's weight is 71 kg (D's weight+3), and the combined weight B, C, and D is 252 kg (weight of A, B, C) - weight of A. Therefore, substituting these into the equation, (252 - A weight + 71)/4 = 79. After solving this equation for A, we get A weight = 75 kg.
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