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# There's a basket containing 10 apples - 7 red and 3 green.

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VP
Joined: 29 Dec 2005
Posts: 1306
There's a basket containing 10 apples - 7 red and 3 green.  [#permalink]

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30 May 2006, 10:58
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There's a basket containing 10 apples - 7 red and 3 green. Upon drawing 2 apples, What's the probability that we get 2 red and 1 green from next drawing of 3 apples?

it is a modified question from the question in the following link: http://www.gmatclub.com/phpbb/viewtopic.php?t=30016

No OA...

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Senior Manager
Joined: 15 Mar 2005
Posts: 407
Location: Phoenix

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30 May 2006, 11:51
Professor wrote:
There's a basket containing 10 apples - 7 red and 3 green. Upon drawing 2 apples, What's the probability that we get 2 red and 1 green from next drawing of 3 apples?

it is a modified question from the question in the following link: http://www.gmatclub.com/phpbb/viewtopic.php?t=30016

No OA...

When you draw 2 apples, you get
1. 1 red and 1 green,
2. Both red,
3. Both green.

1. Probability of 1 red and 1 green
= C(7,1) * C(3,1) / C(10,2) = 21/45=7/15
After this, if we draw 3 more apples, the probability of getting 2R and 1G (from 6R and 2G)= C(6,2)*C(2,1)/C(8,3) = 30/56=15/28
Thus total of this branch = 7/15*15/27=1/4.
2. Probability of both red = C(7,2)*C(3,0)/C(10,2) = 21/45=7/15
Again, after this, if we draw 3 more apples, probability of getting 2R and 1G from 5R and 3G = C(5,2)*C(3,1)/C(8,3)=30/56 = 15/28
Thus total from this branch = 1/4.
3. Probability of both green = C(7,0)*C(3,2)/C(10,2) = 3/45=1/15.
Again, after this, if we draw 3 more apples, probability of getting 2R and 1G from 7R and 1G = C(7,2)*C(1,1)/C(8,3)=21/56.
Thus total probability from this branch = 7/280 = 1/40
Therefore total probability = 1/4+1/4+1/40=21/40.
_________________

Who says elephants can't dance?

SVP
Joined: 30 Mar 2006
Posts: 1676

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31 May 2006, 00:14
can you beleive it Prof, when I read the question on the link yesterday I was solving the question like the way this question has been framed.

Okay let me try

Two apples are drawn hence, both can be red or green or one can be red and one can be green,

--> WHen both are red.
Probability of getting both red = 7C2/10C2 --- eq 1
Probabilty of getting 2 red and 1 green afterwards = 5C2*3C1/8C3 ---eq 2
total P1 = eq1*eq2 ----------- eq3

--> when both green
Probability of getting both green = 2C2/10C2 --- eq 4
Probabilty of getting 2 red and 1 green afterwards = 7C2*1C1/8C3 ---eq 5
total P2 = eq4*eq5 --------------------eq6

--> when one is red and other is green
Probabibilty = 7C1*3C1/10C2 ------- eq 7
Probability of second drawing = 6C2*2C1/8C3 ---- eq8
Total P3 = eq7* eq8

Final P = P1 +p2 +p3
Manager
Joined: 29 Sep 2005
Posts: 124

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31 May 2006, 05:52
There's a basket containing 10 apples - 7 red and 3 green. Upon drawing 2 apples, What's the probability that we get 2 red and 1 green from next drawing of 3 apples?

***********************************************

I came up with 21/40

From 7 red apples choose 2 (2C7) = 21 ---(1)

From 3 green apples choose 1 (1C3) = 1 ---(2)

We have 10 apples in total and we need to choose 3

3C10 = 120 ---(3)

Prob = ((1) + (2))/3

Prob = (21*3)/120 = 21/40
Senior Manager
Joined: 09 Aug 2005
Posts: 272

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31 May 2006, 17:01
Professor wrote:
There's a basket containing 10 apples - 7 red and 3 green. Upon drawing 2 apples, What's the probability that we get 2 red and 1 green from next drawing of 3 apples?

it is a modified question from the question in the following link: http://www.gmatclub.com/phpbb/viewtopic.php?t=30016

No OA...

good job Prof. Salute!!!
we need more of these prima facie scary problems. Looks like a very probable 700 + level question

7c2/10c2 (5c2x3c1/8c3) + 7c1c3c1(6c2x2c1/8c3) + 3c2(7c2x1c1/8c3)=21/40
Non-Human User
Joined: 09 Sep 2013
Posts: 8462
Re: There's a basket containing 10 apples - 7 red and 3 green.  [#permalink]

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21 Nov 2017, 16:26
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--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

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Re: There's a basket containing 10 apples - 7 red and 3 green. &nbs [#permalink] 21 Nov 2017, 16:26
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