题目网址: http://www.puzzleup.com/2019/
http://www.puzzleup.com/2019/puzzle/?14
答题时限: 10月24日７ＰＭ－比赛结束
加分时限: 10月24日７ＰＭ－10月30日６：５９ＰＭ
答对可得基本分１００分。答案可上传５次，每改１次答案从基本分扣２０分。
比赛期间内可随时上传答案，加分时限内答对第ｎ天加（６－ｎ）分
另依题目的难易有额外加分（如有８０％的人这题答错，答对者加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
有本书，A与B以外的所有字母跟空格都被删掉。问单字ABA比单字BABA更早出现的
机率为？
两个字母在该本书出现的机会均等。
以最简分数回答，如 12/23。