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Probability DS

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by 4meonly » Wed Jan 14, 2009 9:36 am
The bowl contains chips of red and green color and no chips of any other color. If two chips are drawn from the basket at random without replacement, what is the probability that both chips will be green?

(1) 20% of all chips in the basket are green
(2) The ratio of the number of red chips to the number of green chips is 4:1
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Source: — Data Sufficiency |
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by bluementor » Wed Jan 14, 2009 11:00 am
T = G + R (total = green + red)

P(both green) = P(1st green)*P(2nd green)

=(G/T)*((G-1)/(T-1))

Notice that both statements give exactly the same info, so choices A, B and C are out. So we work with one statement alone and decide between D and E.

G/T = 1/5
However, (G-1)/(T-1) depends on what the exact values are, which we don't know. Therefore choose E.

-BM-
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Re: Probability DS

by logitech » Wed Jan 14, 2009 11:23 am
Both statements give us the same ration 4X red and X Green

Lets say if there are 5 chips: 4 red and 1 green well we can not even GET two green so PROP = 0 :)

Or lets say we have 400 red and 100 green and now the prob is not zero.

Choose E
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