题目网址: http://www.puzzleup.com/2015/ http://www.puzzleup.com/2015/puzzle/?17 答题时限: 11月19日７ＰＭ－比赛结束（约12月16日） 加分时限: 11月19日７ＰＭ－11月25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）　　 ◆ORDERED CODES How many 25-letter codes formed by using the letters A, B, C, D and E have their letters in alphabetical order? 有多少长 25 字母，使用 A,B,C,D,E 五种字母的编码， 具有编码中的字母是以字母顺序排列的性质？ If the problem was asked for 4-letter codes with the letters A, B, and C, the answer would be 15: 若题目改问长 4 字母，使用 A,B,C 三种字母的话，答案为 15： AAAA, AAAB, AAAC, AABB, AABC, AACC, ABBB, ABBC, ABCC, ACCC, BBBB, BBBC, BBCC, BCCC, CCCC. -- 'Oh, Harry, don't you see?' Hermione breathed. 'If she could have done one thing to make absolutely sure that every single person in this school will read your interview, it was banning it!' ---'Harry Potter and the order of the phoenix', P513 --

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