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probability plz help

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probability plz help

by quantskillsgmat » Fri Mar 09, 2012 10:27 pm
Q two identical urns-black and white each contain 5 blue,5 red and 10 green balls.every ball selected from black urn is immediately returned to the urn,while each ball selected from white urn is removed and placed on a table.If jenny receives a quarter for every blue ball,a dime for every red ball and a nickel for every green ball she selects.what is probability that she will be able to buy a 25 cent candy bar with the proceeds from drawing four balls two from each urn.
a)143/152 b)14/37 c)1 d)0 e)2/3
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by killer1387 » Fri Mar 09, 2012 11:01 pm
quantskillsgmat wrote:Q two identical urns-black and white each contain 5 blue,5 red and 10 green balls.every ball selected from black urn is immediately returned to the urn,while each ball selected from white urn is removed and placed on a table.If jenny receives a quarter for every blue ball,a dime for every red ball and a nickel for every green ball she selects.what is probability that she will be able to buy a 25 cent candy bar with the proceeds from drawing four balls two from each urn.
a)143/152 b)14/37 c)1 d)0 e)2/3
Only way it will not be done is when all the 4 balls are green.
probability for all four green (urns are identical)= 10/20*10/20*10/20*9/19=9/152
required probability= 1-9/152=143/152

hence A.
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