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Tough and tricky 6: Probability of drawing

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Tough and tricky 6: Probability of drawing [#permalink] New post 11 Oct 2009, 18:17
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Question Stats:

33% (00:00) correct 66% (00:36) wrong based on 3 sessions
A bag contains 3 red, 4 black and 2 white balls. What is the probability of drawing a red and a white ball in two successive draws, each ball being put back after it is drawn?
(A) 2/27
(B) 1/9
(C) 1/3
(D) 4/27
(E) 2/9
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Re: Tough and tricky 6: Probability of drawing [#permalink] New post 11 Oct 2009, 18:45
Number of ways to choose Red ball = 3C1
Number of ways to choose White ball = 2C1
Total number of ways to choose 2 balls at random = 9C2

(3C1*2C1)*2C1/9C2 = 1/3
Answer is C.
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Re: Tough and tricky 6: Probability of drawing [#permalink] New post 11 Oct 2009, 23:57
I think its D i.e. 4/27

we can have either RW or WR combination in successive draws.

So the probability will be (3/9 x 2/9) + (2/9 x 3/9) = 4/27

OA pls???????
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Re: Tough and tricky 6: Probability of drawing [#permalink] New post 12 Oct 2009, 04:02
answer should be D

As we are replacing the balls so the probability of drawing two balls at random is 9*9

Ans = 3*2*2/(9*9)
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Re: Tough and tricky 6: Probability of drawing [#permalink] New post 12 Oct 2009, 09:45
Set of Tough & tricky questions is now combined in one thread: tough-tricky-set-of-problms-85211.html

You can continue discussions and see the solutions there.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!! ,11 Mixed Questions NEW!!!, 12 Fresh Meat NEW!!!

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!, 11 New DS set. NEW!!!


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Re: Tough and tricky 6: Probability of drawing [#permalink] New post 11 Feb 2011, 04:43

probability of getting RW = \frac{3}{9}*\frac{2}{9}
we could have RW or WR. in both cases, we'll have a red and a white ball.

total probability = \frac{3}{9}*\frac{2}{9}*2 = \frac{4}{27}

Ans: D
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Re: Tough and tricky 6: Probability of drawing   [#permalink] 11 Feb 2011, 04:43
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