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A jar contains 30 marbles, of which 20 are red and 10 are bl

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A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink] New post 06 Feb 2014, 00:19
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84% (01:53) correct 16% (00:40) wrong based on 135 sessions
The Official Guide For GMAT® Quantitative Review, 2ND Edition

A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9 of the marbles are removed, how many of the marbles left in the jar are red?

(1) Of the marbles removed, the ratio of the number of red ones to the number of blue ones is 2:1.
(2) Of the first 6 marbles removed, 4 are red.

Data Sufficiency
Question: 72
Category: Arithmetic Discrete probability
Page: 158
Difficulty: 600


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Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink] New post 06 Feb 2014, 00:19
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SOLUTION

A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9 of the marbles are removed, how many of the marbles left in the jar are red?

(1) Of the marbles removed, the ratio of the number of red ones to the number of blue ones is 2:1 --> since the total of 9 marbles are removed, then 6 red marbles and 3 blue marbles are removed, thus 20 - 6 = 14 red marbles are left in the jar. Sufficient.

(2) Of the first 6 marbles removed, 4 are red --> we don't know how many of the other 3 marbles removed were red. Not sufficient.

Answer: A.
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Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink] New post 06 Feb 2014, 11:05
A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9 of the marbles are removed, how many of the marbles left in the jar are red?

(1) Of the marbles removed, the ratio of the number of red ones to the number of blue ones is 2:1.
(2) Of the first 6 marbles removed, 4 are red.

Using st1, we can say that total no of marbles removed= sum of individuals marble removed which is equal to 2x:x for red : blue marble
So we have 3x=9 or x=3 and thus remainig red marbles can be calculated
A is sufficient
St 2 says only for first 6 marbles in which 4 are red and the remaining 3 can be any ie all blue or all red or 1 red and 2 blue etc

So A alone is sufficient
600 level is okay

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Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink] New post 06 Feb 2014, 23:36
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No. of marbles = 30, of which Red, R = 20 & Blue, B = 10;
Removed = 9; No. of marbles that will remain = 30 - 9 = 21;

No. of Red marbles remaining in the jar = ?

(1) Removed Marbles- R:B = 2:1; Therefore, 3x = 9; x = 3; So, since we know the no. of removed red marbles as 6, we can find the no. of remaining red marbles = 14;
Sufficient;

(2) Insufficient, since we do not have information about the remaining 3 marbles that have been removed.

Ans is (A).
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Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink] New post 07 Feb 2014, 04:34
Clear A.

B tells nothing about number of Red removed out of 9
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Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink] New post 08 Feb 2014, 05:02
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SOLUTION

A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9 of the marbles are removed, how many of the marbles left in the jar are red?

(1) Of the marbles removed, the ratio of the number of red ones to the number of blue ones is 2:1 --> since the total of 9 marbles are removed, then 6 red marbles and 3 blue marbles are removed, thus 20 - 6 = 14 red marbles are left in the jar. Sufficient.

(2) Of the first 6 marbles removed, 4 are red --> we don't know how many of the other 3 marbles removed were red. Not sufficient.

Answer: A.
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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; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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. ,11 Mixed Questions, 12 Fresh Meat

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Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink] New post 27 May 2014, 07:51
Bunuel wrote:
The Official Guide For GMAT® Quantitative Review, 2ND Edition

A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9 of the marbles are removed, how many of the marbles left in the jar are red?

(1) Of the marbles removed, the ratio of the number of red ones to the number of blue ones is 2:1.
(2) Of the first 6 marbles removed, 4 are red.

Data Sufficiency
Question: 72
Category: Arithmetic Discrete probability
Page: 158
Difficulty: 600


GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project

Each week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project:
1. Please provide your solutions to the questions;
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you!


Although OG categorises it as Probability , I don't think this question will qualify as probability..
Re: A jar contains 30 marbles, of which 20 are red and 10 are bl   [#permalink] 27 May 2014, 07:51
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