數學 槪率問題20分

圖片參考：http://imgcld.yimg.com/8/n/HA09111499/o/20130715200829.jpg


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2013-07-15 20:17:33 補充：
Note that they are conditional probability questions. You only need to assume different outcomes for each stage of calculation and observe how each outcome affect the probabilities of subsequent stages.

2013-07-16 19:28:27 補充：
The probability that the door can be opened is 3/5. If using the correct key to unlock the door is required, then the probability is 2/3*2/5=4/15.

2013-07-17 10:45:25 補充：
用表格比用樹型圖方便兼整潔得多。

用英文問的題目，當然應該用英文作答。

2013-07-18 11:16:43 補充：
如果不懂或者不習慣英文的話，我在此翻譯一下用語作為參考：
Table = 表格；
Correct = 正確的(在此則是相應的鑰匙)；
Draw = 抽取；
Random = 隨機(在此解不偏頗，即每一球獲抽取的機率均等)；
Pool for next draw = 下一輪抽籤的範圍

希望幫到你。

係丫 D人真係會等人答左就刪鬼左佢=,=

2013-07-16 16:14:20 補充：
the probability that a man can open the door by
choosing 2 keys randomly
本身就開左算唔算先,BY A MAN
應該係
(2/3)x2/5
=4/15

2013-07-17 00:54:57 補充：
樹形圖只是個假像=,=
冇人會用樹形圖