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July 15th, 2011, 06:55 PM   #1
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probability

A bag contains balls and it is not known that how many of these are white. balls are drawn and they are found to be white.

What is the probability that all the balls in the bag were white?
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July 15th, 2011, 07:26 PM   #2
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Some additional information is needed to calculate this probability.
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July 15th, 2011, 08:15 PM   #3
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Re: probability

Hello, panky!

Quote:
A bag contains 5 balls and it is not known how many of them are white.
Two balls are drawn and they are found to be white.
What is the probability that all the balls in the bag were white?

Two balls are drawn from rive balls.


[color=beige] .[/color][color=blue][A][/color]

Since two White balls were drawn, the bag contains at least two Whites.

There are four equally likely cases for the contents of the bag:
[color=beige]. . [/color][1] 2 Whites, 3 Blacks
[color=beige]. . [/color][2] 3 Whites, 2 Blacks
[color=beige]. . [/color][3] 4 Whites, 1 Black
[color=beige]. . [/color][5] 5 Whites


[1] 2 Whites, 3 Blacks

[color=beige]. . [/color]


[2] 3 Whites, 2 Blacks

[color=beige]. . [/color]


[3] 4 Whites, 1 Black

[color=beige]. . [/color]


[4] 5 Whites

[color=beige]. . [/color]
[color=beige] .[/color][color=blue][B][/color]

[color=beige] .[/color][color=blue][C][/color]


Substitute [color=blue][B][/color] and [color=blue][C][/color] into [color=blue][A}[/color]:
[color=beige]. . [/color]

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July 18th, 2011, 07:05 PM   #4
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Re: probability

thanks soroban
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