Re: [計量] How many five digit numbers

看板GRE作者 (FLICK)時間16年前 (2009/05/20 22:23), 編輯推噓6(6推 0噓 10→)
留言16則, 7人參與, 最新討論串2/2 (看更多)
※ 引述《hhunhia (ptt)》之銘言： : How many five digit numbers can be formed using the : digits 0, 2, 3, 4 and 5, when repetition is allowed such : that the number formed is divisible by 2 or5 or both? : 答:1500 4x5x5x5x4 = 2000? 第一個0不能選 最後一個3不能選 其他都OK : Four persons enter the lift of a seven storey building at : the ground floor. In how many ways can they get out of : the lift on any floor other than the ground floor? : 答:1296 6x6x6x6=1296 每個人從6樓中選一樓出來都是不同的結果 應該不用考慮出來的順序 : A box contains 5 red and 4 blue balls. In how many : ways can 4 balls be chosen such that there are at most : 3 balls of each colour? : 答:120 C(5,1)C(4,3)+C(5,2)C(4,2)+C(5,3)C(4,1) = 120 這題的前提應該是各種顏色的球都分別不同 不然就是3種可能(3,1)(2,2)(1,3) : 請高手回答~ -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 76.95.151.128 ※ 編輯: Emerica 來自: 76.95.151.128 (05/20 22:24)
推
05/20 22:25, , 1F
要扣掉最後一位是4的組別 共500組
05/20 22:25, 1F
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05/20 22:25, , 2F
所以2000-500=1500
05/20 22:25, 2F
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05/20 22:27, , 3F
4不是可以被二整除嗎?
05/20 22:27, 3F
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05/20 22:28, , 4F
題目有點搞混~第三題應該是藍色要3或紅色要3的組合吧
05/20 22:28, 4F
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05/20 22:30, , 5F
我的理解是最多都不能超過3耶
05/20 22:30, 5F
推
05/20 22:33, , 6F
了解~感謝回答
05/20 22:33, 6F
推
05/20 22:38, , 7F
divisible by 2 or5 or both 題目用or
05/20 22:38, 7F
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05/20 22:39, , 8F
所以只要一個成立即可吧 我是覺得不用扣500
05/20 22:39, 8F
推
05/20 22:52, , 9F
覺得不用扣+1
05/20 22:52, 9F
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05/21 00:16, , 10F
第三題是組合(9顆取4顆)-(紅5顆取4顆)-(藍4顆取4顆)?
05/21 00:16, 10F
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05/21 00:17, , 11F
樓上這也對 應該是一樣的意思
05/21 00:17, 11F
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05/21 00:19, , 12F
嗯 因為最多3顆同色=全取的值扣掉4顆皆為藍/紅
05/21 00:19, 12F
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05/21 00:20, , 13F
你的比較快 哈哈
05/21 00:20, 13F
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05/21 00:22, , 14F
XD 你第一題的解法也比較快 我還在那邊算每種情況= =
05/21 00:22, 14F
推
05/21 12:32, , 15F
感謝回答
05/21 12:32, 15F
推
05/27 14:26, , 16F
所以第一題原PO答案有錯
05/27 14:26, 16F
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文章代碼(AID): #1A5198b5 (GRE)
‣ 更多 Emerica 的文章
文章代碼(AID): #1A5198b5 (GRE)