1. Divide coins into two groups: Divide coins into two groups, each containing five coins. Put the10th coin on the 5th coin in one group (Group A) and the 6th coin on the10th coin in another group (Group B).
2. Balance balance: put Group A on one side of the balance and Group B on the other side of the balance. If the weights of both sides are equal, the faulty coin is at 1-5.
3. Choose the heavier group: If the balance is unbalanced, one of the two groups is heavier. Assuming that Group A is heavier, we can further.
4. Select five coins in the heavier group: Group A is divided into two groups, two of which are faulty coins with unknown weight and the other three are normal coins. Choose three coins and put them on one side of the balance, and the other two on the other side.
5. Balance Balance: If the balance is balanced, it means that the two coins not placed on the balance are faulty coins, and the heavier one is faulty coins. In this way, it can be confirmed that the fault occurred between the 6th 6- 10/0 coin.
6. Unbalanced balance: If the balance is unbalanced, it means that one of the three coins placed on the balance is heavier. In this way, we can determine that the fault occurred in one of the three coins. You can continue to use the same balance method to weigh three coins in groups until you determine the defective coin.
To sum up, through the above steps, we can determine which two coins failed because of measurement difficulties, and at the same time, we can minimize the number of measurements. The principle is to group coins, weigh them with a balance, gradually narrow the scope, and finally determine the defective coins.