GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 25 Mar 2019, 09:05

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 53831
A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post Updated on: 05 Feb 2019, 05:42
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

87% (01:10) correct 13% (01:23) wrong based on 538 sessions

HideShow timer Statistics

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

_________________
New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | 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?
Extra-hard Quant Tests with Brilliant Analytics

Originally posted by Bunuel on 06 Feb 2014, 01:19.
Last edited by Bunuel on 05 Feb 2019, 05:42, edited 1 time in total.
Renamed the topic.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 53831
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 06 Feb 2014, 01:19
2
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.
_________________
New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | 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?
Extra-hard Quant Tests with Brilliant Analytics
Director
Director
User avatar
Joined: 25 Apr 2012
Posts: 680
Location: India
GPA: 3.21
WE: Business Development (Other)
Premium Member Reviews Badge
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 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
Manager
User avatar
Status: GMATting
Joined: 21 Mar 2011
Posts: 105
Concentration: Strategy, Technology
GMAT 1: 590 Q45 V27
GMAT ToolKit User
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 07 Feb 2014, 00:36
1
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
Manager
User avatar
B
Joined: 14 Jan 2013
Posts: 136
Concentration: Strategy, Technology
GMAT Date: 08-01-2013
GPA: 3.7
WE: Consulting (Consulting)
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 07 Feb 2014, 05:34
Clear A.

B tells nothing about number of Red removed out of 9
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 53831
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 08 Feb 2014, 06:02
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.
_________________
New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | 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?
Extra-hard Quant Tests with Brilliant Analytics
Manager
Manager
avatar
Joined: 28 Apr 2014
Posts: 208
GMAT ToolKit User
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 27 May 2014, 08:51
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..
Senior Manager
Senior Manager
User avatar
B
Joined: 10 Mar 2013
Posts: 496
Location: Germany
Concentration: Finance, Entrepreneurship
GMAT 1: 580 Q46 V24
GPA: 3.88
WE: Information Technology (Consulting)
GMAT ToolKit User
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 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: a-department-manager-distributed-a-number-of-pens-pencils-104852.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
User avatar
V
Joined: 02 Sep 2009
Posts: 53831
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 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: a-department-manager-distributed-a-number-of-pens-pencils-104852.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: Ultimate GMAT Quantitative Megathread | 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?
Extra-hard Quant Tests with Brilliant Analytics
Intern
Intern
avatar
Joined: 28 Nov 2015
Posts: 1
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 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?
CEO
CEO
avatar
S
Joined: 20 Mar 2014
Posts: 2624
Concentration: Finance, Strategy
Schools: Kellogg '18 (M)
GMAT 1: 750 Q49 V44
GPA: 3.7
WE: Engineering (Aerospace and Defense)
GMAT ToolKit User Premium Member Reviews Badge
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 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 = 20-4 =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 = 20-6 =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.
Target Test Prep Representative
User avatar
G
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2825
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 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 re-express 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
_________________

Jeffrey Miller

Head of GMAT Instruction

Jeff@TargetTestPrep.com
TTP - Target Test Prep Logo
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 10205
Premium Member
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9  [#permalink]

Show Tags

New post 16 Jan 2019, 13:39
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 Club Bot
Re: A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9   [#permalink] 16 Jan 2019, 13:39
Display posts from previous: Sort by

A jar contains 30 marbles, of which 20 are red and 10 are blue. If 9

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.