kinrex721

引用:

Question:

Bag A contains 7 red balls and 5 blue balls.
Bag B contains 5 red balls and 4 green balls.
One ball is randomly drawn from A and put into B.
Then one ball is drawn from bag B randomly and put into A.
Final, a ball is drawn from A at random.

Find the probability that the final ball drawn from bag A is
    (i) Red
   (ii) Blue
  (iii) Green

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小弟用左好耐時間先計到紅波概率=(93/160), 藍波概率=(37/96)!

所以想起到問下有冇咩快D嘅方法可以計到? 仲有我個紅波藍波答案岩唔岩?

綠波概率係咪可以=(1-P(Red)-P(Blue))? 求教求教, 萬分感謝!

kinrex721

引用:

原帖由 hinokari 於 2011-5-9 06:32 PM 發表
P(R)=(7/12)[(6/10)(7/12)+(4/10)(6/12)]+(5/12)[(5/10)(8/12)+(4/10)(7/12)+(1/10)(7/12)]
=93/160
P(B)=(7/12)(6/10+4/10)(5/12)+(5/12)[(5/10+4/10)(4/12)+(1/10)(5/12)]
=37/96
P(G)=1-P(R)-P(B)=1/30

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上面幅圖幫助好大, 感謝賜教!