| Version 1 (Case 1) | | Rationale |
| First weighing | Put any 3 coins on either side of the scale, leaving you with 2 coins. | If the scale balances, the counterfeit is in one of the two remaining coins. |
| Second weighing | Place the remaining 2 coins, each on either side of the scale. | The lighter coin is the counterfeit |
| Version 1 (Case 2) | | Rationale |
| First weighing | Place any three coins on either side of the scale. | If the scale is unbalanced, the counterfeit is in the lighter group of three coins. |
| Second weighing | Place any 2 coins from the lighter group, each on either side of the scale. | 1) If the scale balances, the counterfeit is the coin that was not weighed. 2) If the scale is not balanced, the lighter coin is counterfeit. |
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