Re: [理工] [離散]-排列組合
※ 引述《Austin9 (奧斯丁)》之銘言:
: 3.In how many ways can two adjacent squares be selected from an 8*8 chessboard?
: ans 8(8-1)+8(8-1) 這也是不懂
: 4.In how many ways can 22 different books be given to 5 student so that 2 of
: them will have books and the order 3 will have 4 books?
: 我的答案是C(22,5)*C(17,5)*C(12,4)*C(8,4)*C(4,4)但答案多了C(5,2)不知道為什麼
: 要多乘這個?
此題題目可能有沒抄到的地方,應該是五人挑兩人送五本書,其他三人是四本,所以要先
乘上C(5,2),先挑兩人各送五本。
也可以先把書分好堆C(22,5)*C(17,5)*C(12,4)*C(8,4)*C(4,4)/2!3!(因為有兩堆個數
一樣,三堆個數一樣),分好後再分給五人,也就是再乘上*5! 效果是跟C(5,2)一樣的
: 5.If we write all decimal number from 1 to 1 million,how many times would we
: have written the digit 9?
: 我的答案是..因為從000000~999999所以是10^6,但答案是10^5,想知道那兒錯了?謝謝
這題我也亂猜,不過我看不太了解問題,是該整數有寫到9算一次,
還是整數有寫到兩個九算兩次。例如989 109809-->兩次?
: 7.Suppose n different games are to distributed among n children.In how many
: ways can this be done so that exactly one child gets no game?
: 不懂答案為什麼是C(n,2)*P(n,n-1)
這次我猜是n*onto(n,n-1),不過這想法應該是錯的
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 112.104.101.170
討論串 (同標題文章)