zkcy401

Among 40students 28 are boy.It is found that 15boys and 5girls wear glasses.If 2students are randomly selected and it is found that these two students are girls,find the probability that only one wear glasses.？ans係7／156

There are 10 orange and 8 apples in a box.If 3 of them are randomly chosen from the box one after another without replacement,find the probability that the first one is apple given that the third one is orange ans係8／17
想問下點用nPr同nCr去諗?
唔該各位

[ 本帖最後由 zkcy401 於 2011-7-7 07:19 PM 編輯 ]

zkcy401

引用:

原帖由 cws~ 於 2011-7-7 06:57 PM 發表 Do you mean 15 students wear glasses?

Sorry我打錯左題目，多謝你提醒

zkcy401

引用:

原帖由 夏娜醬大好 於 2011-7-7 07:10 PM 發表 唔怪得我唔識計啦

對唔住大佬

zkcy401

引用:

原帖由 夏娜醬大好 於 2011-7-7 07:21 PM 發表 條題目有問題題目given果2個人係女仔所以要揾(only 1 wear glasses | both are girls)  7/156係P(only 1 wear glasses and both are girls)

姐係條問題有問題？我改左啦喎

zkcy401

唔該哂各位先 點解你地可以諗得咁easy既=_=

我第二題係咁諗既：
8p1*10p2/18p3 + 8p2*10p1/18p3 = (5/9) p

請問用p有冇錯？

[ 本帖最後由 zkcy401 於 2011-7-7 08:13 PM 編輯 ]

zkcy401

引用:

原帖由 夏娜醬大好 於 2011-7-7 08:24 PM 發表 Instead of 8p1*10p2/18p3 + 8p2*10p1/18p3, you may use:[url=tel8)(16)(10)/18](8)(16)(10)/18[/url]P3Consider A ? O ,We have 8 apples and 10 oranges, so it should be 8*something*10For the " ? " , as 2 fruits have been cho ...

真係唔該哂你