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rock-paper-scissors (game); janken
じゃん拳で誰が最初にやるか決めよう。
Let's decide who goes first with rock-paper-scissors.
子供たちがじゃん拳で遊んでいた。
The children were playing rock-paper-scissors.
順番をじゃん拳で決めることにした。
We decided to determine the order by rock-paper-scissors.