Is it golden or silver? 金か銀か？どちらを言えば有利？

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Three pieces of coins are in the bag. One piece is golden with the both sides, and one piece is silver with the both sides, and, as for one piece, one side is golden, and one side is silver. One piece was just golden when I took it out and put it on the table. I get all the coins when I win the color of the back. By the way, is it advantageous to tell golden or silver or which?

袋の中にコインが３枚入っています。１枚は両面とも金色、１枚は両面とも銀色、１枚は片面が金色で片面が銀色です。今、１枚取り出してテーブルに置くと金色でした。裏の色を当てるとコインを全部もらえます。さて、金か銀か、どちらを言えば有利でしょうか？

考え方と答えAnswer

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スマートホンアプリ「立方体の切り口はどんな形？」（ネット環境でのＦｌａｓｈアニメーション）

スマホ向け解法