Puzzles/Logic puzzles/Scales and Weights/Solution 1

Puzzles | Logic puzzles | Scales and Weights | Solution 1

Weights are: 1, 3, 9, 27

Explanation
You can put the weights on the other side of the balance, therefore subtracting some of the weight from the other side. Using this system the objects can be weighed thus:

1kg = 1kg

2kg = 3kg - 1kg

3kg = 3kg

...

39kg = 27kg + 9kg + 3kg

40kg = 27kg + 9kg + 3kg + 1kg