一年一度的 Puzzleup 今天开始～ 有关规定可以爬文，主要重点是请避免在公开地方讲答案 (直接拿去年第一题的文 repo 了 XD) 题目网址: http://www.puzzleup.com/2015/ http://www.puzzleup.com/2015/puzzle/?1 答题时限: ７月30日７ＰＭ－比赛结束（约12月16日） 加分时限: ７月30日７ＰＭ－８月５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）　　 ◆SAME SUM You randomly select two different 2-digit numbers and calculate their sum. Your friend does the same operations. What is the probability of you and your friend having the same sum? If the problem was asked for two 1-digit numbers, the answer would be 29/405. Enter your answer as a simplified fraction. 你随机选取两个不同的二位数，并计算其和。你的朋友也如此做。 试问你们得到的和相等的机率为何？ 若题目改问两个一位数，则答案为 29/405。 答案请输入最简分数。 -- 'You've sort of made up for it tonight,' said Harry. 'Getting the sword. Finishing the Horcrux. Saving my life.' 'That makes me sound a lot cooler then I was,' Ron mumbled. 'Stuff like that always sounds cooler then it really was,' said Harry. 'I've been trying to tell you that for years.' -- Harry Potter and the Deathly Hollows, P.308 --

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