Find a counterfeit coin from eight one-dollar coins (counterfeit money is heavier than real money). How to find a balance without weight? Please write down the operation process.

Divide eight coins into three groups: the first group, three coins, the second group, three coins, the third group, two coins.

Situation 1. Put the first group and the second group at the two ends of the balance respectively. If it is not balanced, the sinking group must have counterfeit money. Put these three coins into this group1>; Pick two and put them at both ends of the balance. If it is unbalanced, the sinking party is counterfeit money. 2> Pick two coins and put them at both ends of the balance. Both ends of the balance are horizontal, so the third coin left in the group is counterfeit.

Situation 2. Put the first group and the second group at both ends of the balance, and the balance will be balanced, so the counterfeit money is in the third group. Put two coins in the third group at both ends of the balance, and the counterfeit money sinks.

This method only needs to be weighed twice to find counterfeit money.

This kind of topic is the algorithm content of compulsory 3 in senior three.