Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 40413

A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
06 Feb 2014, 01:19
Question Stats:
84% (01:53) correct
16% (00:53) wrong based on 537 sessions
HideShow timer Statistics
The Official Guide For GMAT® Quantitative Review, 2ND EditionA 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 ProjectEach 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!
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
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 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., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Math Expert
Joined: 02 Sep 2009
Posts: 40413

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
06 Feb 2014, 01:19



Director
Joined: 25 Apr 2012
Posts: 728
Location: India
GPA: 3.21
WE: Business Development (Other)

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
06 Feb 2014, 12:05
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 Posted from my mobile device
_________________
“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”



Manager
Status: GMATting
Joined: 21 Mar 2011
Posts: 108
Concentration: Strategy, Technology

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
07 Feb 2014, 00:36
1
This post received KUDOS
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).



Manager
Joined: 14 Jan 2013
Posts: 154
Concentration: Strategy, Technology
GMAT Date: 08012013
GPA: 3.7
WE: Consulting (Consulting)

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
07 Feb 2014, 05:34
Clear A. B tells nothing about number of Red removed out of 9
_________________
"Where are my Kudos" ............ Good Question = kudos
"Start enjoying all phases" & all Sections
__________________________________________________________________ http://gmatclub.com/forum/collectionofarticlesoncriticalreasoning159959.html
http://gmatclub.com/forum/percentages700800levelquestions130588.html
http://gmatclub.com/forum/700to800levelquantquestionwithdetailsoluition143321.html



Math Expert
Joined: 02 Sep 2009
Posts: 40413

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
08 Feb 2014, 06:02



Senior Manager
Joined: 28 Apr 2014
Posts: 282

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
27 May 2014, 08:51
Bunuel wrote: The Official Guide For GMAT® Quantitative Review, 2ND EditionA 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 ProjectEach 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..



Director
Joined: 10 Mar 2013
Posts: 597
Location: Germany
Concentration: Finance, Entrepreneurship
GPA: 3.88
WE: Information Technology (Consulting)

A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
12 Aug 2015, 02:10
Bunuel wrote: 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. Hi Bunuel, why cannot we use the same logic here: adepartmentmanagerdistributedanumberofpenspencils104852.html. By Statement 1: we can also say that the ratio could be 2/1 or 6/3.....I think I'm missing some important point here.
_________________
When you’re up, your friends know who you are. When you’re down, you know who your friends are.
Share some Kudos, if my posts help you. Thank you !
800Score ONLY QUANT CAT1 51, CAT2 50, CAT3 50 GMAT PREP 670 MGMAT CAT 630 KAPLAN CAT 660



Math Expert
Joined: 02 Sep 2009
Posts: 40413

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
16 Aug 2015, 13:14
BrainLab wrote: Bunuel wrote: 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. Hi Bunuel, why cannot we use the same logic here: adepartmentmanagerdistributedanumberofpenspencils104852.html. By Statement 1: we can also say that the ratio could be 2/1 or 6/3.....I think I'm missing some important point here. Here not only we know the ratio of the marbles removed (red:blue = 2:1) but also that the number of removed marbles (9), so 6 red marbles and 3 blue marbles are removed.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
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 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., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 28 Nov 2015
Posts: 1

A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
28 Nov 2015, 18:06
Why is the second statement not sufficient? I set up a proportion like this: 4 Red Removed / 6 Removed = (x) Red Removed / 9 Removed and I got x = 6 which means 6 marbles were red out of the 9 marbles removed. I still dont get why is the second statement is not sufficent?



Math Forum Moderator
Joined: 20 Mar 2014
Posts: 2663
Concentration: Finance, Strategy
GPA: 3.7
WE: Engineering (Aerospace and Defense)

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
28 Nov 2015, 18:24
mahadevanswamygmat wrote: Why is the second statement not sufficient? I set up a proportion like this: 4 Red Removed / 6 Removed = (x) Red Removed / 9 Removed and I got x = 6 which means 6 marbles were red out of the 9 marbles removed. I still dont get why is the second statement is not sufficent? Look at statement 2 this way. You are given that total red = 20, total blue = 10. You have removed 9, out of which 4 are definitely red, 2 are blue. But you do not know anything about the remaining 3 balls. If those 3 remaining balls are blue, you get 5 blue balls and 4 red balls removed, giving you the answer to the question asked = number of red balls remaining = 204 =16. BUT, if those 3 remaining balls are red, you get 3 blue balls and 6 red balls removed, giving you the answer to the question asked = number of red balls remaining = 206 =14. Additionally, you can create couple of other combinations for those 3 remaining balls giving you different answers for number of red balls. This makes statement 2 not sufficient. In your analysis by creating the ratio of red balls to the total balls removed you are assuming that the ONLY case possible is for the proportion of red balls in the first 6 balls to remain the same for the remaining 3 balls. This is a massive assumption that is not supported either by the main question or by statement 2. Your equation will not hold true if all 3 are blue of if the remaining 3 balls are 2 blue and 1 red or 1 blue and 2 red etc. Hope this helps.
_________________
Thursday with Ron updated list as of July 1st, 2015: http://gmatclub.com/forum/consolidatedthursdaywithronlistforallthesections201006.html#p1544515 Rules for Posting in Quant Forums: http://gmatclub.com/forum/rulesforpostingpleasereadthisbeforeposting133935.html Writing Mathematical Formulae in your posts: http://gmatclub.com/forum/rulesforpostingpleasereadthisbeforeposting133935.html#p1096628 GMATCLUB Math Book: http://gmatclub.com/forum/gmatmathbookindownloadablepdfformat130609.html Everything Related to Inequalities: http://gmatclub.com/forum/inequalitiesmadeeasy206653.html#p1582891 Inequalities tips: http://gmatclub.com/forum/inequalitiestipsandhints175001.html Debrief, 650 to 750: http://gmatclub.com/forum/650to750a10monthjourneytothescore203190.html



GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16583

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
09 Apr 2017, 11:46
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). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources



Target Test Prep Representative
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 1212

Re: A jar contains 30 marbles, of which 20 are red and 10 are bl [#permalink]
Show Tags
18 Apr 2017, 16:23
Quote: 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.
We are given that a jar contains 30 marbles, of which 20 are red and 10 are blue. We are also given that 9 marbles are removed, and we need to determine the number of red marbles left in the jar. Statement One Alone: Of the marbles removed, the ratio of the number of red ones to the number of blue ones is 2:1. We can reexpress the ratio of red to blue marbles removed as 2x : x and solve the equation: 2x + x = 9 3x = 9 x = 3 From this we see that 6 red marbles and 3 blue marbles are removed. Thus there are 14 red marbles left in the jar. Statement one alone is sufficient to answer the question. Statement Two Alone: Of the first 6 marbles removed, 4 are red. From this we know that at least 4 red marbles and 2 blue marbles are removed. However, since we don’t know how many of the last 3 marbles are red (or blue), we can’t determine the number of red marbles left in the jar. For example, if the last 3 marbles removed are all red, then 7 red marbles are removed, and thus there are 13 red marbles left in the jar. However, if none of the last 3 marbles are red, then only 4 red marbles are removed, and thus there are 16 red marbles left in the jar. Statement two alone is not sufficient to answer the question. Answer: A
_________________
Jeffery Miller
Head of GMAT Instruction
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions




Re: A jar contains 30 marbles, of which 20 are red and 10 are bl
[#permalink]
18 Apr 2017, 16:23







