ｸｲｽﾞ大陸
千夜一夜
Problem.
Alice and Bob found eleven identical-looking coins, four of which are fake. All of the real coins weigh the same. All of the counterfeit coins weigh the same, but are lighter than the real ones. Alice offered Bob four particular coins. Before agreeing to take them, Bob wants to be sure that they are all real. Can he do this by using the balance scale only twice? He can use any of the eleven coins for weighing.
この前提で，天秤の平均使用回数をしぼってみました．
多分，そういう問題じゃないですよね……
↓Aliceがランダムに選んでofferしてるとして，平均回数をしぼってみるとかですかね……ややこしそう(・o・‖)