It is currently 19 Oct 2017, 08:01

# STARTING SOON:

Live Chat with Cornell Adcoms in Main Chat Room  |  R1 Interview Invites: MIT Sloan Chat  |  UCLA Anderson Chat  |  Duke Fuqua Chat (EA Decisions)

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# The waiter at an expensive restaurant has noticed that 60%

Author Message
TAGS:

### Hide Tags

Intern
Joined: 01 Apr 2013
Posts: 23

Kudos [?]: 66 [3], given: 9

The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

03 Apr 2013, 18:06
3
KUDOS
14
This post was
BOOKMARKED
00:00

Difficulty:

85% (hard)

Question Stats:

52% (01:31) correct 48% (01:12) wrong based on 562 sessions

### HideShow timer Statistics

The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20%
B. 25%
C. 40%
D. 60%
E. 75%
[Reveal] Spoiler: OA

_________________

Last edited by Bunuel on 04 Apr 2013, 03:28, edited 1 time in total.
Renamed the topic and edited the question.

Kudos [?]: 66 [3], given: 9

Verbal Forum Moderator
Joined: 10 Oct 2012
Posts: 627

Kudos [?]: 1355 [0], given: 136

Re: The waiter at an expensive resturant has noticed [#permalink]

### Show Tags

03 Apr 2013, 21:27
Tagger wrote:

The waiter at an expensive resturant has noticed that 60% of the couples order desert and coffee. However, 20% of the couples who order desert dont order coffee. what is the probability that the next couple the waiter seats will not order desert?

A.) 20%
B.) 25%
C.) 40%
D.) 60%
E.) 75%

Let the number of people ordering only desert = d, only ordering coffee be c and ordering both be b. Given that , 20 % of (b+d) = d

or 4d = b.

Thus, as b = 60, d = 15. The total number of people not ordering desert = 100-(60+15) = 25.

B.
_________________

Kudos [?]: 1355 [0], given: 136

Math Expert
Joined: 02 Sep 2009
Posts: 41893

Kudos [?]: 128861 [11], given: 12183

The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

04 Apr 2013, 03:46
11
KUDOS
Expert's post
6
This post was
BOOKMARKED
Tagger wrote:
The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20%
B. 25%
C. 40%
D. 60%
E. 75%

Probably the best way to solve this question is using the double set matrix, as shown below:

From above, we have that 60+0.2x=x --> x=75.

Thus, the probability that the next couple will not order dessert (yellow box) is 100-75=25.

Hope it's clear.

[Reveal] Spoiler:
Attachment:

Coffee and Dessert.png [ 3.79 KiB | Viewed 13805 times ]

_________________

Kudos [?]: 128861 [11], given: 12183

Director
Joined: 03 Aug 2012
Posts: 899

Kudos [?]: 886 [0], given: 322

Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
WE: Information Technology (Investment Banking)
Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

17 Aug 2013, 22:25
Solving for X in the figure shown below we will get Couples for deserts as 75%
And couples not ordering deserts =100-75=25%
Attachments

2set.JPG [ 14 KiB | Viewed 11645 times ]

_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Kudos [?]: 886 [0], given: 322

Senior Manager
Joined: 10 Jul 2013
Posts: 330

Kudos [?]: 419 [0], given: 102

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

18 Aug 2013, 16:31
Tagger wrote:
The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20%
B. 25%
C. 40%
D. 60%
E. 75%

Let, total dessert ordered = T and total couple = 100
From question,
60+20% of T = T
or, T = 75 % ordered dessert.

So next couple will not order dessert = 100-75 = 25 %
_________________

Asif vai.....

Kudos [?]: 419 [0], given: 102

Manager
Joined: 25 Oct 2013
Posts: 169

Kudos [?]: 70 [0], given: 56

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

24 Jan 2014, 06:09
Let total number of couples be 100.

60% order Dessert & Coffee = 60 couples.
20% who order Dessert do not order coffee => 80% who order dessert also order coffee this is given to be 60.
Hence total number of couples who order Dessert is 60*100/80 = 75.
Number of couples who do NOT order Dessert = 100-75 = 25.
The probability that next order will not have dessert is 25%.
_________________

Click on Kudos if you liked the post!

Practice makes Perfect.

Kudos [?]: 70 [0], given: 56

Manager
Joined: 18 Aug 2014
Posts: 130

Kudos [?]: 77 [0], given: 36

Location: Hong Kong
Schools: Mannheim
Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

13 Feb 2015, 00:24
Tagger wrote:
The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20%
B. 25%
C. 40%
D. 60%
E. 75%

I solved this pretty fast this way:

60% dessert and coffee
--> 40% nothing, dessert, or coffee

Let them be the same probability --> 40% / 3 = 13,333%

40% - 13% = 27% --> Answer has to be around this range --> B is closest

Kudos [?]: 77 [0], given: 36

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16670

Kudos [?]: 273 [0], given: 0

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

13 Apr 2016, 05:44
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.
_________________

Kudos [?]: 273 [0], given: 0

Director
Joined: 07 Dec 2014
Posts: 812

Kudos [?]: 247 [0], given: 12

The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

13 Apr 2016, 18:52
let total couples=100
let d=couples who order dessert
d-60=.2d
d=75 couples
100-75=25 couples who don't order dessert
25/100=25%

Kudos [?]: 247 [0], given: 12

Manager
Joined: 30 Dec 2015
Posts: 90

Kudos [?]: 20 [0], given: 153

GPA: 3.92
WE: Engineering (Aerospace and Defense)
The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

08 Oct 2016, 12:50
Tagger wrote:
The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20%
B. 25%
C. 40%
D. 60%
E. 75%

60% order (C+D) i.e Both = 60% of Total
20% of D is without C; i.e. 80% of D also orders C
80% of D = Both
80% of D = 60% of Total
$$\frac{D}{Total} =\frac{60}{80} = \frac{3}{4}$$
Hence, $$\frac{C}{Total} = \frac{1}{4}$$ = 25%
_________________

If you analyze enough data, you can predict the future.....its calculating probability, nothing more!

Kudos [?]: 20 [0], given: 153

SVP
Joined: 05 Jul 2006
Posts: 1750

Kudos [?]: 430 [0], given: 49

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

24 Dec 2016, 13:28
Bunuel wrote:
Tagger wrote:
The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20%
B. 25%
C. 40%
D. 60%
E. 75%

Probably the best way to solve this question is using the double set matrix, as shown below:
Attachment:
Coffee and Dessert.png
From above, we have that 60+0.2x=x --> x=75.

Thus, the probability that the next couple will not order dessert (yellow box) is 100-75=25.

Hope it's clear.

what about (Neither) those who didnt order coffee nor desert

Kudos [?]: 430 [0], given: 49

Math Expert
Joined: 02 Sep 2009
Posts: 41893

Kudos [?]: 128861 [0], given: 12183

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

25 Dec 2016, 01:53
yezz wrote:
Bunuel wrote:
Tagger wrote:
The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20%
B. 25%
C. 40%
D. 60%
E. 75%

Probably the best way to solve this question is using the double set matrix, as shown below:

From above, we have that 60+0.2x=x --> x=75.

Thus, the probability that the next couple will not order dessert (yellow box) is 100-75=25.

Hope it's clear.

what about (Neither) those who didnt order coffee nor desert

To get the probability that the next couple will not order dessert we need the percentage of those who do not order dessert which is 25. Those 25% include Coffee/No Dessert and No Coffee/No Dessert (Neither).
_________________

Kudos [?]: 128861 [0], given: 12183

Intern
Joined: 10 Jan 2017
Posts: 1

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

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

07 Mar 2017, 08:50
Why shouldn't it be solved as
60 + 20 = x.

Posted from my mobile device

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

Math Expert
Joined: 02 Sep 2009
Posts: 41893

Kudos [?]: 128861 [0], given: 12183

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

### Show Tags

07 Mar 2017, 09:20
Nikita16 wrote:
Why shouldn't it be solved as
60 + 20 = x.

Posted from my mobile device

We are given that 20% of the couples who order dessert don't order coffee. We denoted those who order dessert by x, thus those who order dessert but don't order coffee is 20% of that, which is 0.2x.
_________________

Kudos [?]: 128861 [0], given: 12183

Re: The waiter at an expensive restaurant has noticed that 60%   [#permalink] 07 Mar 2017, 09:20
Display posts from previous: Sort by