It is currently 20 Nov 2017, 09:04

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

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If 75 percent of the guests at a certain banquet ordered dessert, what

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

Hide Tags

Expert Post
2 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42264

Kudos [?]: 132782 [2], given: 12372

If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 23 Feb 2011, 04:43
2
This post received
KUDOS
Expert's post
11
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

59% (01:27) correct 41% (01:38) wrong based on 697 sessions

HideShow timer Statistics

The Official Guide For GMAT® Quantitative Review, 2ND Edition

If 75 percent of the guests at a certain banquet ordered dessert, what percent of the guests ordered coffee?

(1) 60 percent of the guests who ordered dessert also ordered coffee.
(2) 90 percent of the guests who ordered coffee also ordered dessert.

Data Sufficiency
Question: 116
Category: Arithmetic Statistics
Page: 161
Difficulty: 550


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!
[Reveal] Spoiler: OA

_________________

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


Last edited by Bunuel on 14 Aug 2017, 08:35, edited 2 times in total.
Edited the question.

Kudos [?]: 132782 [2], given: 12372

Expert Post
4 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42264

Kudos [?]: 132782 [4], given: 12372

If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 23 Feb 2011, 06:28
4
This post received
KUDOS
Expert's post
4
This post was
BOOKMARKED
SOLUTION

If 75 percent of the guests at a certain banquet ordered dessert, what percent of the guests ordered coffee?

Assume there were 100 guests on the banquet. So we have that 75 of them ordered dessert.

(1) 60 percent of the guests who ordered dessert also ordered coffee --> 0.6*75=45 guests ordered both dessert AND coffee, but we still don't know how many guests ordered coffee. Not sufficient.

(2) 90 percent of the guests who ordered coffee also ordered dessert --> 0.9*(coffee) # of guests who ordered both dessert AND coffee. Not sufficient.

(1)+(2) From (1) # of guests who ordered both dessert AND coffee is 45 and from (2) 0.9*(coffee)=45 --> (coffee)=50. Sufficient.

Answer: C.
_________________

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

Kudos [?]: 132782 [4], given: 12372

Expert Post
4 KUDOS received
Veritas Prep GMAT Instructor
User avatar
G
Joined: 16 Oct 2010
Posts: 7738

Kudos [?]: 17815 [4], given: 235

Location: Pune, India
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 23 Feb 2011, 19:11
4
This post received
KUDOS
Expert's post
Baten80 wrote:
IF 75% of guest at a certain banquet ordered dessert,what percent of guest ordered coffee?

1)60%of the guest who ordered dessert also ordered coffee.

2)90%of the guest who ordered coffee also ordered dessert.


In questions involving sets, venn diagrams can be used. They tend to make questions simple.

We need to find the % of total guests (G) who ordered coffee (C). So we want C in terms of G.
Given D = 75% of G

1. 60% of D ordered coffee too
Attachment:
Ques1.jpg
Ques1.jpg [ 9.89 KiB | Viewed 9134 times ]

From the diagram, we see that we do not know what % people ordered only coffee.

2. 90% of C ordered Dessert too.
Attachment:
Ques2.jpg
Ques2.jpg [ 9.41 KiB | Viewed 9133 times ]

From the diagram, we see that we do not know what % people ordered only coffee.

Using both the statements, we see that
60% * 75% * G = 90% * C
Since we get C in terms of G, this is sufficient. Answer (C)
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199

Veritas Prep Reviews

Kudos [?]: 17815 [4], given: 235

3 KUDOS received
TOEFL Forum Moderator
avatar
Joined: 16 Nov 2010
Posts: 1602

Kudos [?]: 600 [3], given: 40

Location: United States (IN)
Concentration: Strategy, Technology
Premium Member Reviews Badge
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 13 Mar 2011, 19:32
3
This post received
KUDOS
1
This post was
BOOKMARKED
Let there be 100 guests

75 guests ordered Dessert


and 60% of 75 = 60/100 * 75 = 45 guests ordered coffee also, but there could be other people from remainig 25 who didn't order dessert (they might or might not have ordered dessert)


So (1) is not suff


Let x guests order coffee, 0.9x ordered dessert too, but we don't know x, so (2) is not sufficient

However, taking (1) and (2) together, 45 = 0.9x, so the answer is C.
_________________

Formula of Life -> Achievement/Potential = k * Happiness (where k is a constant)

GMAT Club Premium Membership - big benefits and savings

Kudos [?]: 600 [3], given: 40

2 KUDOS received
Senior Manager
Senior Manager
User avatar
Joined: 31 Oct 2011
Posts: 484

Kudos [?]: 223 [2], given: 57

Schools: Johnson '16 (M)
GMAT 1: 690 Q45 V40
WE: Asset Management (Mutual Funds and Brokerage)
Premium Member
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 10 Jan 2012, 05:34
2
This post received
KUDOS
Let x be the number of people who chose dessert.
Let y be the number of people who chose coffee
Let z be the number of people who chose neither dessert nor coffee

Given: x=0.75T
T = x+y+z


Stmt 1) 0.6x chose coffee. But nothing is known about y or z.
INSUFF

Stmt 2) 0.9y chose dessert. But nothing is given about x or z.
INSUFF

Combining (1) and (2)
0.6x=0.9y
Thus 0.6*0.75T = 0.9y
Which gives us y=0.5T
Or y=50%.
SUFF

ANS: C
_________________

My Applicant Blog: http://hamm0.wordpress.com/

Kudos [?]: 223 [2], given: 57

Manager
Manager
avatar
Joined: 12 Feb 2012
Posts: 130

Kudos [?]: 63 [0], given: 28

Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 01 Jul 2012, 17:56
Hey Bunuel,

What mistake am I making?

A- # of people who order desert
B- # of people who order coffee
AnB - # of people who order both dessert and coffe

Given: A=75
Statement 1: AnB=.6*70=45
Given that we know AuB=A+B-AnB

100=75+B-45 ----> B=75. Hence statement 1 should be sufficient.

What am I doing wrong here!!!?? So confused? Please help. Thank you!


When I solve this problem by using the 2x2 grid, its obvious that there is not enough information. But when I try to just use the formula it gives me suffient info.

Kudos [?]: 63 [0], given: 28

Expert Post
Veritas Prep GMAT Instructor
User avatar
G
Joined: 16 Oct 2010
Posts: 7738

Kudos [?]: 17815 [0], given: 235

Location: Pune, India
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 01 Jul 2012, 22:25
alphabeta1234 wrote:
Hey Bunuel,

What mistake am I making?

A- # of people who order desert
B- # of people who order coffee
AnB - # of people who order both dessert and coffe

Given: A=75
Statement 1: AnB=.6*70=45
Given that we know AuB=A+B-AnB

100=75+B-45 ----> B=75. Hence statement 1 should be sufficient.

What am I doing wrong here!!!?? So confused? Please help. Thank you!


When I solve this problem by using the 2x2 grid, its obvious that there is not enough information. But when I try to just use the formula it gives me suffient info.


Do you know how many ordered neither? We cannot say that AuB = 100.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199

Veritas Prep Reviews

Kudos [?]: 17815 [0], given: 235

Intern
Intern
avatar
Joined: 04 Jun 2012
Posts: 3

Kudos [?]: 2 [0], given: 3

Concentration: General Management, Finance
GMAT Date: 07-23-2012
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 03 Jul 2012, 07:29
What if there were certain guests who ordered neither coffee nor dessert ?
Would the answer be E in that case?

Kudos [?]: 2 [0], given: 3

Intern
Intern
avatar
Joined: 30 May 2012
Posts: 21

Kudos [?]: 11 [0], given: 0

Concentration: Finance, Strategy
GMAT 1: 730 Q49 V41
GPA: 3.39
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 03 Jul 2012, 08:28
Let D be the event that somebody order the dessert, let C be the event that somebody ordered coffee. From Bayes' Theorem, P(C|D)= P(C)*P(D|C)/P(D) and so P(C)= P(C|D)*P(D) / P(D|C). P(D)=.75 is given.

1. "60%of the guest who ordered dessert also ordered coffee." => P(C|D)=.6. Not sufficient.
2. "90%of the guest who ordered coffee also ordered dessert." => P(D|C)=.9. Not sufficient.
1 and 2: P(C)= P(C|D)*P(D) / P(D|C) = .6*.75/.9 = .5. Sufficient.

C.

Kudos [?]: 11 [0], given: 0

Expert Post
2 KUDOS received
Veritas Prep GMAT Instructor
User avatar
G
Joined: 16 Oct 2010
Posts: 7738

Kudos [?]: 17815 [2], given: 235

Location: Pune, India
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 04 Jul 2012, 02:29
2
This post received
KUDOS
Expert's post
shekharverma wrote:
What if there were certain guests who ordered neither coffee nor dessert ?
Would the answer be E in that case?


We have already taken into account that there could be some people who ordered neither. In fact, if you see the answer you get, 75% ordered dessert, 50% ordered coffee and 45% ordered both. This means that 75 + 50 - 45 = 80% people ordered at least one of dessert and coffee. The rest of the 20% people ordered neither dessert nor coffee. They could have ordered something else or nothing - it doesn't matter to us. The answer remains (C).
From both the statements, we see that 45% of all = 90% of C which means C is half of all. Hence C = 50%. Our questions asks the % of all who ordered coffee. We get that as 50%. We are not concerned about the remaining people.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199

Veritas Prep Reviews

Kudos [?]: 17815 [2], given: 235

Intern
Intern
avatar
Joined: 07 Feb 2012
Posts: 14

Kudos [?]: 1 [0], given: 1

Concentration: Strategy
GMAT 1: 720 Q48 V41
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 12 Aug 2012, 04:20
Bunuel wrote:
Baten80 wrote:
IF 75% of guest at a certain banquet ordered dessert,what percent of guest ordered coffee?

1)60%of the guest who ordered dessert also ordered coffee.

2)90%of the guest who ordered coffee also ordered dessert.


IF 75% of guest at a certain banquet ordered dessert, what percent of guest ordered coffee?

Assume there were 100 guests on the banquet. So we have that 75 of them ordered dessert.

(1) 60% of the guest who ordered dessert also ordered coffee --> 0.45*75=45 guests ordered both dessert AND coffee, but we still don't know how many guests ordered coffee. Not sufficient.

(2) 90% of the guest who ordered coffee also ordered dessert --> 0.9*(coffee) # of guests who ordered both dessert AND coffee. Not sufficient.

(1)+(2) From (1) # of guests who ordered both dessert AND coffee is 45 and from (2) 0.9*(coffee)=45 --> (coffee)=50. Sufficient.

Answer: C.



Hi

Just to clear a major fundamental misunderstanding I have here - why didn't we use the formula method to solve this problem?So:

Total guests=Coffee + Dessert - Both --(a)

Let guests be 100. Hence dessert =75. From (1), Both = 45

Hence from equation (a) Coffee should = 30..

I know this is wrong, but I need someone to pinpoint why my approach is wrong here

Thanks guys

Kudos [?]: 1 [0], given: 1

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42264

Kudos [?]: 132782 [0], given: 12372

Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 12 Aug 2012, 07:21
deliverance wrote:
Bunuel wrote:
Baten80 wrote:
IF 75% of guest at a certain banquet ordered dessert,what percent of guest ordered coffee?

1)60%of the guest who ordered dessert also ordered coffee.

2)90%of the guest who ordered coffee also ordered dessert.


IF 75% of guest at a certain banquet ordered dessert, what percent of guest ordered coffee?

Assume there were 100 guests on the banquet. So we have that 75 of them ordered dessert.

(1) 60% of the guest who ordered dessert also ordered coffee --> 0.45*75=45 guests ordered both dessert AND coffee, but we still don't know how many guests ordered coffee. Not sufficient.

(2) 90% of the guest who ordered coffee also ordered dessert --> 0.9*(coffee) # of guests who ordered both dessert AND coffee. Not sufficient.

(1)+(2) From (1) # of guests who ordered both dessert AND coffee is 45 and from (2) 0.9*(coffee)=45 --> (coffee)=50. Sufficient.

Answer: C.



Hi

Just to clear a major fundamental misunderstanding I have here - why didn't we use the formula method to solve this problem?So:

Total guests=Coffee + Dessert - Both --(a)

Let guests be 100. Hence dessert =75. From (1), Both = 45

Hence from equation (a) Coffee should = 30..

I know this is wrong, but I need someone to pinpoint why my approach is wrong here

Thanks guys


It should be {Total}={Coffee}+{Dessert}-{Both}+{Neither}. Since we don't know how many of the guests ordered neither coffee nor dessert we cannot calculate the number of guests who ordered coffee based on the info from (1).

Check Karishma's post above about the same issue: if-75-of-guest-at-a-certain-banquet-ordered-dessert-what-109889.html#p1101532
_________________

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

Kudos [?]: 132782 [0], given: 12372

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42264

Kudos [?]: 132782 [0], given: 12372

Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 28 Feb 2014, 03:55
Expert's post
22
This post was
BOOKMARKED
The Official Guide For GMAT® Quantitative Review, 2ND Edition

If 75 percent of the guests at a certain banquet ordered dessert, what percent of the guests ordered coffee?

(1) 60 percent of the guests who ordered dessert also ordered coffee.
(2) 90 percent of the guests who ordered coffee also ordered dessert.

Data Sufficiency
Question: 116
Category: Arithmetic Statistics
Page: 161
Difficulty: 550


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!

_________________

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

Kudos [?]: 132782 [0], given: 12372

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42264

Kudos [?]: 132782 [0], given: 12372

Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 01 Mar 2014, 06:11
Expert's post
5
This post was
BOOKMARKED
SOLUTION

If 75 percent of the guests at a certain banquet ordered dessert, what percent of the guests ordered coffee?

Assume there were 100 guests on the banquet. So we have that 75 of them ordered dessert.

(1) 60 percent of the guests who ordered dessert also ordered coffee --> 0.6*75=45 guests ordered both dessert AND coffee, but we still don't know how many guests ordered coffee. Not sufficient.

(2) 90 percent of the guests who ordered coffee also ordered dessert --> 0.9*(coffee) # of guests who ordered both dessert AND coffee. Not sufficient.

(1)+(2) From (1) # of guests who ordered both dessert AND coffee is 45 and from (2) 0.9*(coffee)=45 --> (coffee)=50. Sufficient.

Answer: C.
_________________

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

Kudos [?]: 132782 [0], given: 12372

Intern
Intern
avatar
Joined: 25 Apr 2013
Posts: 20

Kudos [?]: 10 [0], given: 358

Location: India
Schools: Wharton Exec '17
GPA: 4
WE: Engineering (Transportation)
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 01 Mar 2014, 06:50
Bunuel, can we assume the number of guests as 100??...what if the number of guest is 200?
coz in the question, it is given as percent. please clarify...thanks...

Kudos [?]: 10 [0], given: 358

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42264

Kudos [?]: 132782 [0], given: 12372

Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 01 Mar 2014, 06:53
srinjoy28 wrote:
Bunuel, can we assume the number of guests as 100??...what if the number of guest is 200?
coz in the question, it is given as percent. please clarify...thanks...


We are asked to find what percent of the guests ordered coffee. You can assume any number for the number of guests and you should get the same answer. Try it with 200 to check.

Hope it helps.
_________________

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

Kudos [?]: 132782 [0], given: 12372

Manager
Manager
avatar
Joined: 18 May 2014
Posts: 62

Kudos [?]: 20 [0], given: 6

Location: United States
Concentration: General Management, Other
GMAT Date: 07-31-2014
GPA: 3.99
WE: Analyst (Consulting)
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 18 May 2014, 09:57
Let D = total who ordered dessert.
Let C = total who ordered coffee.
Let B = total who ordered both dessert and coffee.
Plug in guests = 100.

Then D = .75*100 = 75.

Statement 1:
Tells us that B = .6*75 = 45. Not sufficient to determine C.

Statement 2:
Tells us the .9C = B. Not sufficient to determine C.

Statements 1 and 2 together:
.9C = 45.
C = 50.
Sufficient.

The correct answer is C.

Kudos [?]: 20 [0], given: 6

Current Student
avatar
Joined: 13 Aug 2009
Posts: 13

Kudos [?]: 9 [0], given: 27

Location: United States
Concentration: Strategy, General Management
GMAT 1: 680 Q45 V38
WE: Project Management (Computer Software)
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 13 Nov 2014, 17:57
Hi Bunuel,

I am stuck at the following equation, which I am not able to understand. Please clarify.

Assuming total # of guests = 100
Guests who ordered dessert (D) = 75
Guests who ordered coffee (C) = x

Stmt (1) D + C = 45
So, 75 + x - 45 = 100
=> x = 100 - 30 = 70

Is this deduction incorrect?

Thanks,
S.

Kudos [?]: 9 [0], given: 27

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42264

Kudos [?]: 132782 [0], given: 12372

Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 14 Nov 2014, 02:26
Caeser wrote:
Hi Bunuel,

I am stuck at the following equation, which I am not able to understand. Please clarify.

Assuming total # of guests = 100
Guests who ordered dessert (D) = 75
Guests who ordered coffee (C) = x

Stmt (1) D + C = 45
So, 75 + x - 45 = 100
=> x = 100 - 30 = 70

Is this deduction incorrect?

Thanks,
S.


Yes, because there might be people who ordered neither coffee nor dessert:

{Total} = {Dessert} + {Coffee} - {Both} + {Neither}
100 = 75 + {Coffee} - 45 + {Neither}

As you can see we cannot find {Coffee}.
_________________

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

Kudos [?]: 132782 [0], given: 12372

Expert Post
1 KUDOS received
Math Revolution GMAT Instructor
User avatar
P
Joined: 16 Aug 2015
Posts: 4326

Kudos [?]: 3041 [1], given: 0

GPA: 3.82
Premium Member CAT Tests
Re: If 75 percent of the guests at a certain banquet ordered dessert, what [#permalink]

Show Tags

New post 22 Sep 2015, 04:49
1
This post received
KUDOS
Expert's post
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem.
Remember equal number of variables and independent equations ensures a solution.


If 75% of guest at a certain banquet ordered dessert, what percent of guest ordered coffee?

(1) 60%of the guest who ordered dessert also ordered coffee.

(2) 90%of the guest who ordered coffee also ordered dessert.

Transforming the original condition and the question, we have the below 2by2 table that is common in GMAT math test.

Attachment:
GC DS Baten80 If 75% of guest ar a certain banquet(20150921).jpg
GC DS Baten80 If 75% of guest ar a certain banquet(20150921).jpg [ 39.43 KiB | Viewed 1401 times ]


from above, since the question is x+y(as it asks the %), we have 2 variables (x,y) and therefore need 2 equations to match the number of variables and equations. Since there is 1 each in 1) and 2), C has high probability of being the answer. Using both 1) & 2) together,
75G*0.6=45G leads to x=45, 0.9(45+y)G=45G leads to y=5. Therefore x+y=45+5=50 and the conditions are sufficient. Therefore the answer is C.

Normally for cases where we need 2 more equations, such as original conditions with 2 variable, or 3 variables and 1 equation, or 4 variables and 2 equations, we have 1 equation each in both 1) and 2). Therefore C has a high chance of being the answer, which is why we attempt to solve the question using 1) and 2) together. Here, there is 70% chance that C is the answer, while E has 25% chance. These two are the key questions. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer according to DS definition, we solve the question assuming C would be our answer hence using ) and 2) together. (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Find a 10% off coupon code for GMAT Club members.
“Receive 5 Math Questions & Solutions Daily”
Unlimited Access to over 120 free video lessons - try it yourself
See our Youtube demo

Kudos [?]: 3041 [1], given: 0

Re: If 75 percent of the guests at a certain banquet ordered dessert, what   [#permalink] 22 Sep 2015, 04:49

Go to page    1   2    Next  [ 25 posts ] 

Display posts from previous: Sort by

If 75 percent of the guests at a certain banquet ordered dessert, what

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


GMAT Club MBA Forum Home| About| Terms and Conditions| 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®.