Oct 22 08:00 AM PDT  09:00 AM PDT Join to learn strategies for tackling the longest, wordiest examples of Counting, Sets, & Series GMAT questions Oct 22 09:00 AM PDT  10:00 AM PDT Watch & learn the Do's and Don’ts for your upcoming interview Oct 22 08:00 PM PDT  09:00 PM PDT On Demand for $79. For a score of 4951 (from current actual score of 40+) AllInOne Standard & 700+ Level Questions (150 questions) Oct 23 08:00 AM PDT  09:00 AM PDT Join an exclusive interview with the people behind the test. If you're taking the GMAT, this is a webinar you cannot afford to miss! Oct 26 07:00 AM PDT  09:00 AM PDT Want to score 90 percentile or higher on GMAT CR? Attend this free webinar to learn how to prethink assumptions and solve the most challenging questions in less than 2 minutes. Oct 27 07:00 AM EDT  09:00 AM PDT Exclusive offer! Get 400+ Practice Questions, 25 Video lessons and 6+ Webinars for FREE.
Author 
Message 
TAGS:

Hide Tags

Manager
Status: Do and Die!!
Joined: 15 Sep 2010
Posts: 244

There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
25 Nov 2010, 19:05
Question Stats:
50% (01:44) correct 50% (01:32) wrong based on 290 sessions
HideShow timer Statistics
There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes? 15 30 45 60 120
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
I'm the Dumbest of All !!



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9701
Location: Pune, India

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
25 Nov 2010, 21:33
shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 Consider one hand that gets shaken as one event. One person shakes his hand with three other people so 3 events take place per person. In all 10*3 = 30 events take place. But two hands make one handshake. So 30 of these events will make 15 handshakes. Question: Substitute 5 in place of 10. What do you get? Why?
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >



Manager
Status: Do and Die!!
Joined: 15 Sep 2010
Posts: 244

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
26 Nov 2010, 10:13
why do we have to divide 30 by 2... substituting 5 with 10, i would get 5 which is half of 10.
_________________
I'm the Dumbest of All !!



Manager
Joined: 27 Jul 2010
Posts: 136
Location: Prague
Schools: University of Economics Prague

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
26 Nov 2010, 12:57
Hello Karishma Can you please explain further? I think I don't quite understand it. Is is so, that when you want to shake hand with 3 people, the number of persons in the group has to be even and equal or greater than 4? Thanks VeritasPrepKarishma wrote: shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 Consider one hand that gets shaken as one event. One person shakes his hand with three other people so 3 events take place per person. In all 10*3 = 30 events take place. But two hands make one handshake. So 30 of these events will make 15 handshakes. Question: Substitute 5 in place of 10. What do you get? Why?
_________________
You want somethin', go get it. Period!



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9701
Location: Pune, India

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
26 Nov 2010, 15:47
shrive555 wrote: why do we have to divide 30 by 2... substituting 5 with 10, i would get 5 which is half of 10. Consider you and I shake hands. When I count 30, I have counted it twice. Once for you, and once for me. But it is actually just one handshake. Each one of those 30 events was one hand that was shaken. Two of those events make one handshake so we divide by 2.
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9701
Location: Pune, India

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
26 Nov 2010, 16:07
craky wrote: Hello Karishma Can you please explain further? I think I don't quite understand it. Is is so, that when you want to shake hand with 3 people, the number of persons in the group has to be even and equal or greater than 4? Thanks VeritasPrepKarishma wrote: shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 Consider one hand that gets shaken as one event. One person shakes his hand with three other people so 3 events take place per person. In all 10*3 = 30 events take place. But two hands make one handshake. So 30 of these events will make 15 handshakes. Question: Substitute 5 in place of 10. What do you get? Why? Ok Look. 4 people: shrive555, craky, karishma and Mr X We have to shake hands in this group such that each person shakes hands with 3 people. So shrive555 starts: shrive555  craky : 1 handshake but 2 hands were shaken. shrive555's and craky's shrive555  karishma : 1 handshake but 2 hands were shaken. shrive555's and karishma's shrive555  Mr X : 1 handshake but 2 hands were shaken. shrive555's and Mr X's Now shrive555 has shaken hands with 3 people. There were 3 handshakes. But 6 hands were shaken. Now, when all 4 of us shake hands with 3 people, each person's hand will be shaken 3 times. i.e. in all 12 hands will be shaken. But they will add up to only 6 handshakes. The other 3 handshakes will be: craky  karishma craky  Mr X karishma  Mr X So all of us have shaken hands with exactly 3 people. Similarly when there are 10 people, each person shakes his hand 3 times. So in all 30. But 2 of these hands combined to make one handshake. So we will get only 15 total handshakes. Now when there are 5 people and each person has to shake hands with exactly 3 people, each person will shake his hand 3 times. We will have total 15 hands that will be shaken. So how many handshakes does it make? 7.5? That is not possible. This is because it is not possible for 5 people to shake hands such that each person will shake hands with exactly 3 people. Can you think of the condition which must be satisfied such that it is possible that each person shakes hands with exactly 3 people? (craky, you are there. Just think some more to be clear.)
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >



Intern
Joined: 23 Jul 2013
Posts: 14

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
19 Mar 2016, 15:08
VeritasPrepKarishma wrote: shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 Consider one hand that gets shaken as one event. One person shakes his hand with three other people so 3 events take place per person. In all 10*3 = 30 events take place. But two hands make one handshake. So 30 of these events will make 15 handshakes. Question: Substitute 5 in place of 10. What do you get? Why? [/quote] Ok Look. 4 people: shrive555, craky, karishma and Mr X We have to shake hands in this group such that each person shakes hands with 3 people. So shrive555 starts: shrive555  craky : 1 handshake but 2 hands were shaken. shrive555's and craky's shrive555  karishma : 1 handshake but 2 hands were shaken. shrive555's and karishma's shrive555  Mr X : 1 handshake but 2 hands were shaken. shrive555's and Mr X's Now shrive555 has shaken hands with 3 people. There were 3 handshakes. But 6 hands were shaken. Now, when all 4 of us shake hands with 3 people, each person's hand will be shaken 3 times. i.e. in all 12 hands will be shaken. But they will add up to only 6 handshakes. The other 3 handshakes will be: craky  karishma craky  Mr X karishma  Mr X So all of us have shaken hands with exactly 3 people. Similarly when there are 10 people, each person shakes his hand 3 times. So in all 30. But 2 of these hands combined to make one handshake. So we will get only 15 total handshakes. Now when there are 5 people and each person has to shake hands with exactly 3 people, each person will shake his hand 3 times. We will have total 15 hands that will be shaken. So how many handshakes does it make? 7.5? That is not possible. This is because it is not possible for 5 people to shake hands such that each person will shake hands with exactly 3 people. Can you think of the condition which must be satisfied such that it is possible that each person shakes hands with exactly 3 people? (craky, you are there. Just think some more to be clear.)[/quote] Hi Karishma, Take this forward for 10 individuals we have the following scenario: 1 & 2,  1st unique handshake 1 & 3,  2nd unique handshake 1 & 4,  3rd unique handshake 2 & 1, 2 & 3,  4th unique handshake 2 & 4,  5th unique handshake 3 & 1, 3 & 2, 3 & 4,  6th unique handshake Case for individual number 5, 6, 7 and 8 will also make 6 unique handshakes. So in all 12 upto now. For individual number 9 and 10. 9 & 10  11th unique handshake 10 & 9 Now, individuals numbered 9 and 10 don't even end up meeting the condition of "exactly 3 handshakes". I selected 15, as it was the closest (to 11 unique handshakes) choice. Can you please assist? Thanks.



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9701
Location: Pune, India

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
19 Mar 2016, 20:36
Meetup wrote: Hi Karishma,
Take this forward for 10 individuals we have the following scenario:
1 & 2,  1st unique handshake 1 & 3,  2nd unique handshake 1 & 4,  3rd unique handshake 2 & 1, 2 & 3,  4th unique handshake 2 & 4,  5th unique handshake 3 & 1, 3 & 2, 3 & 4,  6th unique handshake
Case for individual number 5, 6, 7 and 8 will also make 6 unique handshakes. So in all 12 upto now.
For individual number 9 and 10.
9 & 10  11th unique handshake 10 & 9
Now, individuals numbered 9 and 10 don't even end up meeting the condition of "exactly 3 handshakes".
I selected 15, as it was the closest (to 11 unique handshakes) choice. Can you please assist? Thanks.
Since it is given that each person does shake hands with exactly 3 people, it will certainly be possible. Here is one such instance: 1&2 3&4 5&6 7&8 9&10 (Each person shakes hands once) 1&3 2&5 4&7 6&9 8&10 (Each person shakes hand with another person) 1&5 2&9 3&7 4&10 6&8 (Each person shakes hands with yet another person)
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >



Intern
Joined: 06 Feb 2016
Posts: 19

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
24 Apr 2017, 05:12
Hello Karishma! Quote: Question: Substitute 5 in place of 10. What do you get? Why?
9. Let's say we have 5 people in the room: A, B, C, D, E. And there are handshakes: A: B, C, D B: C, D, E C: D, E D: E So, there are will be 3+3+2+1=9 handshakes in total. Is that correct?



Senior Manager
Joined: 03 Apr 2013
Posts: 264
Location: India
Concentration: Marketing, Finance
GPA: 3

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
12 Jun 2017, 11:58
VeritasPrepKarishma wrote: shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 Consider one hand that gets shaken as one event. One person shakes his hand with three other people so 3 events take place per person. In all 10*3 = 30 events take place. But two hands make one handshake. So 30 of these events will make 15 handshakes. Question: Substitute 5 in place of 10. What do you get? Why? Can you please suggest more questions like this one to practice? I struggled with this one really..my approach was different for solving this. Your approach is really creative, and without having solved something of this sort before or read about the method you used, I wouldn't have been able to do this question. Please also suggest something to read. Thank you so much
_________________
Spread some love..Like = +1 Kudos



Math Expert
Joined: 02 Sep 2009
Posts: 58398

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
12 Jun 2017, 13:36
ShashankDave wrote: VeritasPrepKarishma wrote: shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 Consider one hand that gets shaken as one event. One person shakes his hand with three other people so 3 events take place per person. In all 10*3 = 30 events take place. But two hands make one handshake. So 30 of these events will make 15 handshakes. Question: Substitute 5 in place of 10. What do you get? Why? Can you please suggest more questions like this one to practice? I struggled with this one really..my approach was different for solving this. Your approach is really creative, and without having solved something of this sort before or read about the method you used, I wouldn't have been able to do this question. Please also suggest something to read. Thank you so much http://gmatclub.com/forum/howmanydiag ... 01540.htmlhttp://gmatclub.com/forum/if10persons ... 10622.htmlhttp://gmatclub.com/forum/10businesse ... 26163.htmlhttp://gmatclub.com/forum/howmanydiff ... 29992.htmlhttp://gmatclub.com/forum/15chessplay ... 55939.htmlhttp://gmatclub.com/forum/thereare5c ... 27235.htmlhttp://gmatclub.com/forum/ifeachparti ... 42222.htmlhttp://gmatclub.com/forum/thereare8t ... 34582.htmlhttp://gmatclub.com/forum/thereare8t ... 32366.htmlhttp://gmatclub.com/forum/inakickball ... 61846.htmlhttps://gmatclub.com/forum/if11person ... 89706.htmlhttps://gmatclub.com/forum/6peoplemee ... 18398.htmlhttps://gmatclub.com/forum/thereare10 ... 05386.htmlhttps://gmatclub.com/forum/therearein ... 07442.htmlhttps://gmatclub.com/forum/duringasea ... 59677.htmlhttps://gmatclub.com/forum/sixthreere ... 31082.htmlHope it helps.
_________________



VP
Joined: 07 Dec 2014
Posts: 1224

There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
12 Jun 2017, 18:55
shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 if each of the 10 had shaken hands once with 9 others, there would have been 10*9/2, or 45 total handshakes, but, because only one third (3 out of 9) of possible handshakes take place, there are only one third (15 out of 45) total handshakes 15 A



Current Student
Joined: 06 Nov 2016
Posts: 102
Location: India
GPA: 2.8

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
13 Jun 2017, 00:12
craky wrote: Hello Karishma Can you please explain further? I think I don't quite understand it. Is is so, that when you want to shake hand with 3 people, the number of persons in the group has to be even and equal or greater than 4? Thanks VeritasPrepKarishma wrote: shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
15 30 45 60 120 Consider one hand that gets shaken as one event. One person shakes his hand with three other people so 3 events take place per person. In all 10*3 = 30 events take place. But two hands make one handshake. So 30 of these events will make 15 handshakes. Question: Substitute 5 in place of 10. What do you get? Why? If all 5 people shook hands with the other 4  a total of 10 handshakes would have taken place (5*4/2). now for each to shake exactly three hands there would be a total of 9 or more handshakes as either one would shake with only two or one would shake with four. please explain



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 15308
Location: United States (CA)

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
11 Feb 2018, 13:45
Hi All, Since the answer choices are so "spread out", there's an interesting way to get to the correct answer by avoiding complex math and using "brute force" and a comparison: We're told that there are 10 people in the room and that each person shakes hands with 3 other people. Let's say there were 4 people, who we'll call A, B, C and D. The handshakes would be: AB AC AD BC BD CD In this situation, each person shook hands with 3 people and there was a total of 6 handshakes. If we TRIPLED the number of people, then we'd have 12 people, and we'd have TRIPLE the handshakes: 6 x 3 = 18. Since we have FEWER than 12 people, we'll have FEWER than 18 handshakes. There's only one answer that fits: Final Answer: GMAT assassins aren't born, they're made, Rich
_________________
Contact Rich at: Rich.C@empowergmat.comThe Course Used By GMAT Club Moderators To Earn 750+ souvik101990 Score: 760 Q50 V42 ★★★★★ ENGRTOMBA2018 Score: 750 Q49 V44 ★★★★★



GMAT Club Legend
Joined: 12 Sep 2015
Posts: 4016
Location: Canada

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
22 Apr 2018, 06:35
shrive555 wrote: There are 10 people in a room. If each person shakes hands with exactly 3 other people, what is the total number of handshakes?
A) 15 B) 30 C) 45 D) 60 E) 120 Here's an approach that doesn't require any counting techniques: Each person shakes hands with exactly 3 other peopleSo, we have 10 people and each experiences 3 handshakes for a TOTAL of 30 handshakes. IMPORTANT: at this point, we need to recognize that every handshake has been counted TWICE. For example, if Person A and Person B shake hands, then Person A counts it as a handshake, AND Person B also counts it as a handshake. Of course only one handshake occurred. To account for the DUPLICATION, we'll divide 30 by 2 to get 15 Answer: A Cheers, Brent
_________________
Test confidently with gmatprepnow.com



Senior Manager
Joined: 17 Mar 2014
Posts: 429

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
21 Oct 2018, 09:16
StaicyT wrote: Hello Karishma! Quote: Question: Substitute 5 in place of 10. What do you get? Why?
9. Let's say we have 5 people in the room: A, B, C, D, E. And there are handshakes: A: B, C, D B: C, D, E C: D, E D: E So, there are will be 3+3+2+1=9 handshakes in total. Is that correct? VeritasKarishma, To answer :: Substitute 5 in place of 10. What do you get? Why? Will there be only 6 handshakes ? A: B, C, D >3 B: C, D >2 C: D 1 D: E =0 because A, B, C, and D already shake hands with each other and only 3 exactly handshakes are allowed. So no one is left to shake hand with E. Is my thinking correct ?



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9701
Location: Pune, India

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
23 Oct 2018, 04:05
ammuseeru wrote: StaicyT wrote: Hello Karishma! Quote: Question: Substitute 5 in place of 10. What do you get? Why?
9. Let's say we have 5 people in the room: A, B, C, D, E. And there are handshakes: A: B, C, D B: C, D, E C: D, E D: E So, there are will be 3+3+2+1=9 handshakes in total. Is that correct? VeritasKarishma, To answer :: Substitute 5 in place of 10. What do you get? Why? Will there be only 6 handshakes ? A: B, C, D >3 B: C, D >2 C: D 1 D: E =0 because A, B, C, and D already shake hands with each other and only 3 exactly handshakes are allowed. So no one is left to shake hand with E. Is my thinking correct ? Note this: AB, CD, EA, BC, AC, BE, DE A, B, C and E have 3 handshakes each but D has only 2 handshakes. It is not possible for D to have a 3rd handshake. That is why we get 7.5 when we use the formal method.
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >



Senior Manager
Joined: 09 Jun 2014
Posts: 352
Location: India
Concentration: General Management, Operations

There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
23 Oct 2018, 05:40
VeritasKarishma ,Chetan sir, I need your help in this!! I understood the explanation that you gave but this reminded me of an OG problem There are 8 teams in a certain league and each team plays each of the other teams exactly once. If each game is played by 2 teams, what is the total number of games played? A. 15 B. 16 C. 28 D. 56 E. 64 This problem I understand we have to make selection of 2 players out of 10.. So I was little confused ..isn't it similar to the handsake problem?? If Team A player say 8th player plays with the 7th player that means 7th has played with 8th..(much like handsake problem) The only difference is in handsake is done by 3 people and here game is played by two teams.. If I use that approach..which I am very tempted to..I land up with a wrong answer.. Can you please help me here?



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 15308
Location: United States (CA)

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
23 Oct 2018, 11:27
Hi prabsahi, The question that you're asking about is discussed here: https://gmatclub.com/forum/thereare8 ... 34582.htmlGMAT assassins aren't born, they're made, Rich
_________________
Contact Rich at: Rich.C@empowergmat.comThe Course Used By GMAT Club Moderators To Earn 750+ souvik101990 Score: 760 Q50 V42 ★★★★★ ENGRTOMBA2018 Score: 750 Q49 V44 ★★★★★



Senior Manager
Joined: 09 Jun 2014
Posts: 352
Location: India
Concentration: General Management, Operations

Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
Show Tags
23 Oct 2018, 12:29
EMPOWERgmatRichC wrote: Hi prabsahi, The question that you're asking about is discussed here: https://gmatclub.com/forum/thereare8 ... 34582.htmlGMAT assassins aren't born, they're made, Rich Thanks EMPOWERgmatRichC!! Can that problems be worked based on the problem discussion which we have in the current thread?




Re: There are 10 people in a room. If each person shakes hands with exactl
[#permalink]
23 Oct 2018, 12:29



Go to page
1 2
Next
[ 22 posts ]



