MATH 問題(Probability0

2009-03-05 2:30 am

There are 3 white balls and 2 black balls in a bag. Two balls are drawn from the bag. It is know that one of the balls is black, find the probability that the other ball is white.

個ANSWER 係 6/7,但係唔知點計出尼,HELPＭＥ

回答 (1)

Gabriella Montez

2009-03-05 3:10 am

✔ 最佳答案

Solution:
P ( 1 black and 1 white balls ) / P ( at least one black ball )
= [ ( 3 / 5 )( 2 / 4 ) + ( 2 / 5 )( 3 / 4 ) ] / [ 1 - ( 3 / 5 )( 2 / 4 ) ]
= 0.6 / 0.7
= 6 / 7

2009-03-04 19:13:56 補充：
Remarks for conditional probability:
Given event B has occurred, the conditional prob. for event A to occur
= No. of outcomes favourable to A and B / Total no. of possible outcomes favourable to B

2009-03-04 19:15:04 補充：
In the above, the [No. of outcomes favourable to A and B] is [1 black and 1 white balls] while the [Total no. of possible outcomes favourable to B ] is [ at least one black ball ].

參考: My Maths Knowledge

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