It is currently 19 Sep 2017, 12:03

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 10 persons meet at a reunion and each person shakes hands

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Manager
Manager
avatar
Joined: 05 Sep 2007
Posts: 144

Kudos [?]: 50 [0], given: 0

Location: New York
If 10 persons meet at a reunion and each person shakes hands [#permalink]

Show Tags

New post 31 Mar 2008, 18:19
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

100% (00:42) correct 0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If 10 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes?
(A) 10•9•8•7•6•5•4•3•2•1
(B) 10•10
(C) 10•9
(D) 45
(E) 36

Kudos [?]: 50 [0], given: 0

Director
Director
avatar
Joined: 10 Sep 2007
Posts: 936

Kudos [?]: 327 [0], given: 0

Re: PS: handshake [#permalink]

Show Tags

New post 31 Mar 2008, 18:32
People shaking hands are expressed by = n(n-1)/2
As there are 10 people so = 10*9/2 = 45

Answer D.

Kudos [?]: 327 [0], given: 0

Senior Manager
Senior Manager
User avatar
Joined: 01 Feb 2005
Posts: 271

Kudos [?]: 108 [0], given: 1

Re: PS: handshake [#permalink]

Show Tags

New post 31 Mar 2008, 18:44
45

First person shakes hands with 9 people
2nd person shakes hands with 8 people
and so on.... all the way to 1

Add the sum = 45 (D) 45

Kudos [?]: 108 [0], given: 1

Manager
Manager
avatar
Joined: 14 Jun 2007
Posts: 168

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

Location: Vienna, Austria
Re: PS: handshake [#permalink]

Show Tags

New post 20 Oct 2008, 01:38
guys
can someone tell me why: n(n-1)/2 is used to get the number of handshakes?

isn´t that a modification of the sum formula n*(n+1)/2 ?

thanks for clarification

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

SVP
SVP
avatar
Joined: 17 Jun 2008
Posts: 1540

Kudos [?]: 278 [0], given: 0

Re: PS: handshake [#permalink]

Show Tags

New post 20 Oct 2008, 05:35
domleon wrote:
guys
can someone tell me why: n(n-1)/2 is used to get the number of handshakes?

isn´t that a modification of the sum formula n*(n+1)/2 ?

thanks for clarification



More than the formula, I will go by actual numbers to be added. Since, it is 9+8+7+....+1 hence, sum = 9*10/2.

Kudos [?]: 278 [0], given: 0

VP
VP
User avatar
Joined: 30 Jun 2008
Posts: 1033

Kudos [?]: 688 [0], given: 1

Re: PS: handshake [#permalink]

Show Tags

New post 20 Oct 2008, 05:57
scthakur wrote:

More than the formula, I will go by actual numbers to be added. Since, it is 9+8+7+....+1 hence, sum = 9*10/2.


Why do we add here ? why not multiplication? 9*8*7.....
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Kudos [?]: 688 [0], given: 1

Current Student
avatar
Joined: 28 Dec 2004
Posts: 3354

Kudos [?]: 315 [0], given: 2

Location: New York City
Schools: Wharton'11 HBS'12
Re: PS: handshake [#permalink]

Show Tags

New post 20 Oct 2008, 07:58
i am not a big fan formulas...but its good to understand them...

lets see..what is the total number of hand shakes..well its N*(N-1) number of total possibilites..but keep in mind it takes 2 people to shake hands as such..the total number of handshakes will be n*(n-1)/2

10*9/2=45

Kudos [?]: 315 [0], given: 2

SVP
SVP
avatar
Joined: 17 Jun 2008
Posts: 1540

Kudos [?]: 278 [0], given: 0

Re: PS: handshake [#permalink]

Show Tags

New post 20 Oct 2008, 11:12
amitdgr wrote:
scthakur wrote:

More than the formula, I will go by actual numbers to be added. Since, it is 9+8+7+....+1 hence, sum = 9*10/2.


Why do we add here ? why not multiplication? 9*8*7.....


It is because, each person shakes hand only once.

Kudos [?]: 278 [0], given: 0

VP
VP
avatar
Joined: 17 Jun 2008
Posts: 1378

Kudos [?]: 390 [0], given: 0

Re: PS: handshake [#permalink]

Show Tags

New post 20 Oct 2008, 13:45
el1981 wrote:
If 10 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes?
(A) 10•9•8•7•6•5•4•3•2•1
(B) 10•10
(C) 10•9
(D) 45
(E) 36

selecting pair of people from 10 : 10C2 =10*9/2 =45

IMO D
_________________

cheers
Its Now Or Never

Kudos [?]: 390 [0], given: 0

VP
VP
User avatar
Joined: 05 Jul 2008
Posts: 1403

Kudos [?]: 423 [0], given: 1

Re: PS: handshake [#permalink]

Show Tags

New post 21 Oct 2008, 20:17
amitdgr wrote:
scthakur wrote:

More than the formula, I will go by actual numbers to be added. Since, it is 9+8+7+....+1 hence, sum = 9*10/2.


Why do we add here ? why not multiplication? 9*8*7.....


We don't multiply because we are enumerating the number of hand shakes A can possibly do, B can do and so on on until J, if there are A to J people.

Kudos [?]: 423 [0], given: 1

VP
VP
User avatar
Joined: 30 Jun 2008
Posts: 1033

Kudos [?]: 688 [0], given: 1

Re: PS: handshake [#permalink]

Show Tags

New post 21 Oct 2008, 21:04
icandy wrote:
amitdgr wrote:
scthakur wrote:

More than the formula, I will go by actual numbers to be added. Since, it is 9+8+7+....+1 hence, sum = 9*10/2.


Why do we add here ? why not multiplication? 9*8*7.....


We don't multiply because we are enumerating the number of hand shakes A can possibly do, B can do and so on on until J, if there are A to J people.


thanks icandy ... i sort of get it now :)
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Kudos [?]: 688 [0], given: 1

Re: PS: handshake   [#permalink] 21 Oct 2008, 21:04
Display posts from previous: Sort by

If 10 persons meet at a reunion and each person shakes hands

  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®.