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by tsmith93 » Fri Mar 26, 2010 5:35 am
A jar has 5 marbles, 1 of each of the colors red, white, blue, and yellow. If 4 marbles are removed from the jar, what is the probability that the yellow marble was removed?

(a) 1/20
(b) 1/5
(c) 1/4
(d) 4/5
(e) 5/4
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by eaakbari » Fri Mar 26, 2010 5:47 am
I think you forgot to list one more colour of marbles.
Nonetheless

Instead of finding probability that the yellow marble was removed lets find the probability that it was not removed

that is P(Yel left) = 4/5 *3/4 * 2/3 *1/2

P(yel gone) = 1 - p (yel left )

= 96 / 120 =4/5

Therefore OA = D
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by thephoenix » Fri Mar 26, 2010 8:44 am
tot # of ways for selecting 4 marbles out if 5 is 5c4=5 ways

# of selecting 4 marbles out of 4 ( leaving yellow marble) is 4c4=1 way
so P of not picking yellow marble=1/5
hence P of picking a yellow marble=1-1/5=4/5
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by harshavardhanc » Fri Mar 26, 2010 1:19 pm
tsmith93 wrote:A jar has 5 marbles, 1 of each of the colors red, white, blue, and yellow. If 4 marbles are removed from the jar, what is the probability that the yellow marble was removed?

(a) 1/20
(b) 1/5
(c) 1/4
(d) 4/5
(e) 5/4
there are 5C4 or 5 ways to select 4 colored balls out of 5.

out these 5 ways, each color will be present in 4 of the ways. hence, required prob = 4/5 .
Regards,
Harsha
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