9 Weights

Of 9 identical weights, 8 weigh the same, while one (a counterfeit) is lighter than the others. The counterfeit can be found in two weighings one a plain balance with no markings on it.

How many weights are put on both pans during the 1st weighing, and how many are put during the 2nd weighing?

Explanations

Divide 9 weights into 3 groups of 3 weights each.

Weighing 1. Weigh any two groups against each other. If the pans balance (1A), one of the 3 weights not on the balance is counterfeit. If one of the pans goes up (1A), one of the 3 weights on it is counterfeit.

Weighing 2. Of the 3 weights that include the counterfeit, weigh any one weight against another 1. Outcomes of the 2A and 2B would decide the counterfeit weight as is shown in the diagram.

Please, note, the right column B has the same approach in logic if the right pan goes up at the weighing stage 1B.

Puzzle 9 Weights