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Puzzles/Logic puzzles/Scales and Weights/Solution 2
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Puzzles | Logic puzzles | Scales and Weights | Solution 2
Weights are: 2, 6, 18, 54
Explanation
Put 2kg on one side, your item on the other. If item is less than 2kg, it is 1 kg. if it's more:
Put 6kg on one side, your item and 2kg on the other. If item and 2kg are less than 6kg, item is 3kg. Else:
Put 6kg on one side, your item on the other. If item is less than 6kg, it's 5kg.
...
This way you can weigh up to 81kg.