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

It is currently 22 Feb 2019, 08:32

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 in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
  • Free GMAT RC Webinar

     February 23, 2019

     February 23, 2019

     07:00 AM PST

     09:00 AM PST

    Learn reading strategies that can help even non-voracious reader to master GMAT RC. Saturday, February 23rd at 7 AM PT
  • FREE Quant Workshop by e-GMAT!

     February 24, 2019

     February 24, 2019

     07:00 AM PST

     09:00 AM PST

    Get personalized insights on how to achieve your Target Quant Score.

David and Rachel are getting married. The extended family wants to hav

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

Hide Tags

 
Retired Moderator
avatar
Joined: 29 Apr 2015
Posts: 839
Location: Switzerland
Concentration: Economics, Finance
Schools: LBS MIF '19
WE: Asset Management (Investment Banking)
GMAT ToolKit User Premium Member
David and Rachel are getting married. The extended family wants to hav  [#permalink]

Show Tags

New post 02 Jul 2015, 11:04
2
6
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

62% (01:47) correct 38% (01:39) wrong based on 120 sessions

HideShow timer Statistics

David and Rachel are getting married. The extended family wants to have its picture taken, but David's father is unwilling to stand next to Rachel's mother. How many options does the photographer have to arrange the 10 family members in a row for the picture?

A. 9!
B. 9×8!
C. 8×9!
D. 10!/2!
E. 10!

_________________

Saving was yesterday, heat up the gmatclub.forum's sentiment by spending KUDOS!

PS Please send me PM if I do not respond to your question within 24 hours.

Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 53067
Re: David and Rachel are getting married. The extended family wants to hav  [#permalink]

Show Tags

New post 02 Jul 2015, 11:14
reto wrote:
David and Rachel are getting married. The extended family wants to have its picture taken, but David's father is unwilling to stand next to Rachel's mother. How many options does the photographer have to arrange the 10 family members in a row for the picture?

A. 9!
B. 9×8!
C. 8×9!
D. 10!/2!
E. 10!


In how many ways David's father and Rachel's mother can stand together? Consider them as one unit: {F, M}. So, we'd have 9 units {F, M}, 1, 2, 3, 4, 5, 6, 7, 8, which can be arranged in 9! ways. David's father and Rachel's mother within their unit can be arranged in 2! ways. Therefore, David's father and Rachel's mother can stand together in 9!*2! ways.

Total - Restriction =

= 10! - 9!*2! =

= 9!(10 - 2!) =

= 8*9!.

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

Retired Moderator
avatar
Joined: 29 Apr 2015
Posts: 839
Location: Switzerland
Concentration: Economics, Finance
Schools: LBS MIF '19
WE: Asset Management (Investment Banking)
GMAT ToolKit User Premium Member
Re: David and Rachel are getting married. The extended family wants to hav  [#permalink]

Show Tags

New post 20 Jul 2015, 11:58
1
reto wrote:
David and Rachel are getting married. The extended family wants to have its picture taken, but David's father is unwilling to stand next to Rachel's mother. How many options does the photographer have to arrange the 10 family members in a row for the picture?

A. 9!
B. 9×8!
C. 8×9!
D. 10!/2!
E. 10!


I just wanted to add how you get to the final 8x9! because I was struggling with it:

Total Options are 10!
Forbidden Options are 9!*2

Good Options are 10!-9!*2 which can be rewritten as:

10*9! - 2*9!

It is then possible to extract 9! as the common factor:

9!(10-2) = 9! * 8
_________________

Saving was yesterday, heat up the gmatclub.forum's sentiment by spending KUDOS!

PS Please send me PM if I do not respond to your question within 24 hours.

CEO
CEO
avatar
S
Joined: 20 Mar 2014
Posts: 2629
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: David and Rachel are getting married. The extended family wants to hav  [#permalink]

Show Tags

New post 20 Jul 2015, 12:07
reto wrote:
reto wrote:
David and Rachel are getting married. The extended family wants to have its picture taken, but David's father is unwilling to stand next to Rachel's mother. How many options does the photographer have to arrange the 10 family members in a row for the picture?

A. 9!
B. 9×8!
C. 8×9!
D. 10!/2!
E. 10!


I just wanted to add how you get to the final 8x9! because I was struggling with it:

Total Options are 10!
Forbidden Options are 9!*2

Good Options are 10!-9!*2 which can be rewritten as:

10*9! - 2*9!

It is then possible to extract 9! as the common factor:

9!(10-2) = 9! * 8


Additionally, I like using the slot method to look at the possible, allowed and forbidden cases.

Consider 10 slots for 10 members.

_ _ _ _ _ _ _ _ _ _ We can arrange these 10 members in 10! ways (=10P10).

NOw consider 1 scenario in which the dad (D) stands next to mom (M) : DM + 8 slots for the rest of the members: D M _ _ _ _ _ _ _ _ , we can arrange these in 9! X 2! ways ( 2! ways for arranging D and M into DM or MD and 9! to arrange 8! members + 1 combined (D and M) slots)

Thus we have the total number of arrangements possible = 10! - 9!X2 = 10X9! - 9!X2 = 9! (8), C is the correct answer.
Director
Director
User avatar
S
Status: Come! Fall in Love with Learning!
Joined: 05 Jan 2017
Posts: 542
Location: India
Premium Member
Re: David and Rachel are getting married. The extended family wants to hav  [#permalink]

Show Tags

New post 21 Mar 2017, 02:03
reto wrote:
David and Rachel are getting married. The extended family wants to have its picture taken, but David's father is unwilling to stand next to Rachel's mother. How many options does the photographer have to arrange the 10 family members in a row for the picture?

A. 9!
B. 9×8!
C. 8×9!
D. 10!/2!
E. 10!


10 member can be arranged in 10! ways
Let those two stand together. We will consider them as one entity with 2! way to arrange within themselves

total number of people = 8 +1 = 9. ways of arranging - 9!

therefore total ways of arranging with this restriction = 10! - 9!2! = 8.9!
_________________

GMAT Mentors
Image

Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 9894
Premium Member
Re: David and Rachel are getting married. The extended family wants to hav  [#permalink]

Show Tags

New post 01 Feb 2019, 01:57
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

GMAT Club Bot
Re: David and Rachel are getting married. The extended family wants to hav   [#permalink] 01 Feb 2019, 01:57
Display posts from previous: Sort by

David and Rachel are getting married. The extended family wants to hav

  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®.