※ 引述《ivanos (Peel quickly and see)》之銘言： : 朋友寫信問我一個輕鬆有趣的題目，跟大家分享一下 : Mr. Short, his sister, his son, and his daughter are fond of golf and often : play together. The following statements are true of their foursome: : (1) The best player's twin and the worst player are of the opposite sex. : (2) The best player and the worst player are the same age. : Which one of the foursome is the best player? 由條件一知道，有一組人是雙胞胎 先以年齡分類，Short, his sister一組，the son and the daughter一組推想 會發現沒有任何人同時滿足兩個條件 (雙胞胎是父親和姑姑，則不可能有任一人和子女同年；反之亦然) 所以雙胞胎一定是子女，然後Short's sister的年齡和Short的子女相同 才會出現又有雙胞胎又有第三人與他們同齡的狀況 此時根據條件一知道，best player在雙胞胎裡面， 所以根據條件二知道，worst player可先確定為姑姑 這時從條件一得知，姑姑和兒子性別相反， 所以best player是女兒。 --

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