Puzzleup 2019 (14) TWO LETTER BOOK - 拼圖

題目網址: http://www.puzzleup.com/2019/
http://www.puzzleup.com/2019/puzzle/?14
答題時限: 10月24日７ＰＭ－比賽結束
加分時限: 10月24日７ＰＭ－10月30日６：５９ＰＭ

答對可得基本分１００分。答案可上傳５次，每改１次答案從基本分扣２０分。　
比賽期間內可隨時上傳答案，加分時限內答對第ｎ天加（６－ｎ）分　 　　 　　
另依題目的難易有額外加分（如有８０％的人這題答錯，答對者加８０分）　　　

◆TWO LETTER BOOK

In a book, all letters and spaces except the letters A and B have been
deleted. What is the probability that the word ABA appears before the
word BABA?

Both letters are equally likely to appear in the book.

Enter your answer as a simplified fraction. Example:12/23

有本書，A與B以外的所有字母跟空格都被刪掉。問單字ABA比單字BABA更早出現的
機率為？

兩個字母在該本書出現的機會均等。

以最簡分數回答，如 12/23。

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