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Q-30

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by engg.manik » Sat Oct 10, 2009 5:46 am
30.There are 10 marble balls, including 5 green, 3 blue, and 2 red, in a container. One ball is picked out then put back, then another ball is selected. What is the probability that a green ball and a blue ball will be selected?
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by dmateer25 » Sat Oct 10, 2009 6:29 am
If the order of the balls doesn't matter then it would be

2 * (5/10) * (3/10) = 3/10
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by NikolayZ » Sat Oct 10, 2009 6:54 am
Hey mate.
dmateer25, nice one ! =)
i calculated 3/20.
Forgetting the matter of order is just freaking me out.
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Re: Q-30

by Brent@GMATPrepNow » Sat Oct 10, 2009 7:08 am
engg.manik wrote:30.There are 10 marble balls, including 5 green, 3 blue, and 2 red, in a container. One ball is picked out then put back, then another ball is selected. What is the probability that a green ball and a blue ball will be selected?
P(blue and green)= P(1st is blue and 2nd is green OR 1st is green and 2nd is blue)
= P(1st is blue and 2nd is green) + P(1st is green and 2nd is blue)
= (3/10)(5/10) + (3/10)(5/10)
= 3/10
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