[中學] 排列組合 裝信問題
有五封不同的信
分別對應五個不同的信封
請問恰好裝錯四封的方法有幾種？
沒頭緒啊..
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04/21 18:40, , 1F
04/21 18:40, 1F
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04/21 18:47, , 2F
04/21 18:47, 2F
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04/21 18:49, , 3F
04/21 18:49, 3F
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04/21 18:50, , 4F
04/21 18:50, 4F
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04/21 18:51, , 5F
04/21 18:51, 5F
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04/21 18:54, , 6F
04/21 18:54, 6F
→
04/21 18:55, , 7F
04/21 18:55, 7F
→
04/21 21:46, , 8F
04/21 21:46, 8F
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04/21 21:50, , 9F
04/21 21:50, 9F