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

It is currently 12 Nov 2019, 12:12

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

If 11 persons meet at a reunion and each person shakes hands exactly o

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

Hide Tags

Find Similar Topics 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 58989
If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 08 Dec 2014, 06:26
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

61% (00:47) correct 39% (00:54) wrong based on 185 sessions

HideShow timer Statistics

Tough and Tricky questions: Combinations.



If 11 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) 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
B) 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
C) 11 × 10
D) 55
E) 45

Kudos for a correct solution.

Source: Chili Hot GMAT

_________________
Manager
Manager
avatar
Joined: 21 Sep 2012
Posts: 206
Location: United States
Concentration: Finance, Economics
Schools: CBS '17
GPA: 4
WE: General Management (Consumer Products)
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 08 Dec 2014, 06:29
1
11C2 = 11*10/2 = 11*5 = 55
Ans - D
Manager
Manager
avatar
Joined: 04 Oct 2013
Posts: 150
Location: India
GMAT Date: 05-23-2015
GPA: 3.45
GMAT ToolKit User Reviews Badge
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 08 Dec 2014, 07:06
1
If 11 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) 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
B) 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
C) 11 × 10
D) 55
E) 45


Total number of handshakes = \(C^{11}_{2}\)\(= \frac{11*10}{2}=55\)

Answer: D
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 58989
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 09 Dec 2014, 06:51
Bunuel wrote:

Tough and Tricky questions: Combinations.



If 11 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) 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
B) 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
C) 11 × 10
D) 55
E) 45

Kudos for a correct solution.

Source: Chili Hot GMAT


The correct answer is D.
_________________
Intern
Intern
User avatar
Joined: 08 Jul 2012
Posts: 46
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 09 Dec 2014, 07:00
2
If 11 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes?

1st person will have 10 handshakes, 2nd will have 9, ....10th will have 1 and 11th will have 0
= 10+9+8+7+6+5+4+3+2+1 = 55

if we generalize this: if there are n people then there will be n(n-1)/2 handshakes.

Ans.D) 55
_________________
Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time. - Thomas A. Edison
Senior Manager
Senior Manager
avatar
P
Joined: 27 Aug 2014
Posts: 357
Location: Netherlands
Concentration: Finance, Strategy
Schools: LBS '22, ISB '21
GPA: 3.9
WE: Analyst (Energy and Utilities)
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 19 Oct 2015, 11:05
JJo wrote:
If 11 persons meet at a reunion and each person shakes hands exactly once with each of the others, what is the total number of handshakes?

1st person will have 10 handshakes, 2nd will have 9, ....10th will have 1 and 11th will have 0
= 10+9+8+7+6+5+4+3+2+1 = 55

if we generalize this: if there are n people then there will be n(n-1)/2 handshakes.

Ans.D) 55



JJo I think you meant n(n+1)/2 handshakes.
EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 15430
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 19 Oct 2015, 11:44
1
2
Hi All,

This question doesn't require any special math formulas - you just need to take some notes and do a bit of arithmetic.

We're told that 11 people will each shake hands with one another. We're asked how many handshakes actually occur:

I'm going to name the 11 people ABCDE FGHIJ and K

A shakes the hands of the 10 other people.
B has ALREADY shook hands with A, so B shakes 9 'new' hands.
C has ALREADY shook hands with A and B, so C shakes 8 'new hands.
Etc.

You should notice that with each new person, the number of 'new' handshakes decreases by 1. This gives us...

10+9+8+7+6+5+4+3+2+1+0

For a total of 55

Final Answer:

GMAT assassins aren't born, they're made,
Rich
_________________
Contact Rich at: Rich.C@empowergmat.com
Image


The Course Used By GMAT Club Moderators To Earn 750+

souvik101990 Score: 760 Q50 V42 ★★★★★
ENGRTOMBA2018 Score: 750 Q49 V44 ★★★★★
Manager
Manager
avatar
Joined: 13 Sep 2015
Posts: 82
Location: United States
Concentration: Social Entrepreneurship, International Business
GMAT 1: 770 Q50 V45
GPA: 3.84
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 21 Oct 2015, 17:59
Bunuel wrote:

Tough and Tricky questions: Combinations.



If 11 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) 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
B) 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
C) 11 × 10
D) 55
E) 45

Kudos for a correct solution.

Source: Chili Hot GMAT


its the sum from 1 to 10, coz the person can't shake hands with himself then each next to him loses 1 chance to shake hands because he's shaken hands with the one counted:

10+9+8+......+1=(10+1)*10/2=55

this shortcut applies to other questions the like, such as games between two teams blablabla
Intern
Intern
User avatar
Joined: 09 May 2012
Posts: 18
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 23 Mar 2016, 08:00
santorasantu : This can be made simple. Derive your own formula wherever needed.
Case 1.Two men would need only a single hand shake.
Case 2.Three men would need three hand shakes.
Your formula must satisfy above two cases.
Hence it is n(n-1)/2.
Case 1. 2*1/2 = 1
Case 2. 3*2/2 = 3

Our case : 11*10/2 = 55 . Answer is (D).
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 13566
Re: If 11 persons meet at a reunion and each person shakes hands exactly o  [#permalink]

Show Tags

New post 18 May 2019, 23:23
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: If 11 persons meet at a reunion and each person shakes hands exactly o   [#permalink] 18 May 2019, 23:23
Display posts from previous: Sort by

If 11 persons meet at a reunion and each person shakes hands exactly o

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





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