中五數學問題-概率 - Ans.fyi 參考答案

中五數學問題-概率

Lau

2009-01-05 8:44 am

There are two bags. Bag A contains 1 red marble,1 blue marble and 2
green marbles .Bag B contains 2 red marbles and 2 blue marbles.
Vincent chooses one bag at random and then a marble is drawn
randomly from the selected bag.

(a)Find the probability that the marble drawn is green
(b)Find the probability that the marble drawn is red

Suppose Vincent puts the marble drawn from the selected bag into
the other bag,and then randomly draws a marble from that other bag.
What is the probability that the second marble is of

(a)the same colour as the first marble
(b) different colours from the first marble

回答 (1)

myisland8132

2009-01-05 9:00 am

✔ 最佳答案

(a)
Probability
=(1/2)(2/4)+(1/2)(0)
=1/4
(b)
Probability
=(1/2)(1/4)+(1/2)(2/4)
=3/8
(a)
Probability
=(1/2)(1/4)(3/5)+(1/2)(1/4)(3/5)+(1/2)(2/4)(1/5)+(1/2)(2/4)(2/5)+(1/2)(2/4)(1/5)
=14/40
=7/20
(b)
Probability
=1-7/20
=13/20

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