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# In box A, there are 10 red marbles, 10 green marbles and 10 yellow

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Senior CR Moderator
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In box A, there are 10 red marbles, 10 green marbles and 10 yellow  [#permalink]

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14 Dec 2016, 06:47
3
00:00

Difficulty:

65% (hard)

Question Stats:

58% (02:28) correct 42% (02:40) wrong based on 88 sessions

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In box A, there are 10 red marbles, 10 green marbles and 10 yellow marbles. Jack takes turn in picking randomly a marble from that box. What is the probability that Jack picks 4 marbles that have the same color?

A. 2/87
B. 16/29
C. 2/261
D. 28/1131
E. 28/3393

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Re: In box A, there are 10 red marbles, 10 green marbles and 10 yellow  [#permalink]

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14 Dec 2016, 09:50
1
Number of marbles available = 30
Number of ways of selecting 4 marbles out of 30 = 30C4

Number of ways of selecting -
all red marbles = 10C4
all green marbles = 10C4
all yellow marbles = 10C4

Probability = (10C4 + 10C4 + 10C4)/30C4 = (3*10C4)/30C4 = 2/87

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Re: In box A, there are 10 red marbles, 10 green marbles and 10 yellow  [#permalink]

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14 Dec 2016, 11:06
Can you please explain what is the expression 10C4?
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Re: In box A, there are 10 red marbles, 10 green marbles and 10 yellow  [#permalink]

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14 Dec 2016, 11:12
dhimank wrote:
Can you please explain what is the expression 10C4?

$$nCr = \frac{(n!)}{{(n - r)! * r!}}$$

10C4 = (10 * 9 * 8 * 7)/(4 * 3 * 2 * 1)
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Joined: 09 Jan 2016
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Re: In box A, there are 10 red marbles, 10 green marbles and 10 yellow  [#permalink]

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14 Dec 2016, 11:15
Perfect. Thanks!! Makes much more sense now.
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Re: In box A, there are 10 red marbles, 10 green marbles and 10 yellow  [#permalink]

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10 Mar 2019, 11:26
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: In box A, there are 10 red marbles, 10 green marbles and 10 yellow   [#permalink] 10 Mar 2019, 11:26
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