Author 
Message 
TAGS:

Hide Tags

Senior Manager
Status: mba here i come!
Joined: 07 Aug 2011
Posts: 264

Re: Overlapping Sets Problem [#permalink]
Show Tags
27 Aug 2011, 12:22
1
This post received KUDOS
1
This post was BOOKMARKED
those who play single instrument = 20 those who don't play a single instrument (play 2 or 3) = 3520 = 15 those who play 2 instruments = 153 = 12 (3 play all three instruments)
_________________
press +1 Kudos to appreciate posts Download Valuable Collection of Percentage Questions (PS/DS)



Intern
Joined: 29 Aug 2011
Posts: 23

Re: Overlapping Sets Problem [#permalink]
Show Tags
06 Sep 2011, 12:43
I worked on this using Venn Diagram. Got the answer 6 in one shot. The answer is how many play 2 instruments so we need to count the people who also play 3 instruments ( given already 3).



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7440
Location: Pune, India

Re: Overlapping Sets Problem [#permalink]
Show Tags
06 Sep 2011, 21:57
MBAhereIcome wrote: those who play single instrument = 20 those who don't play a single instrument (play 2 or 3) = 3520 = 15
those who play 2 instruments = 153 = 12 (3 play all three instruments) The 35 that you counted: 10 + 11 + 14 double counts the number of people who play only 2 instruments and triple counts the number of people who play all 3 instruments. The circle of 10 of piano includes the red and the green region. The circle of 11 of Guitar includes the red and green region too. Similarly, the circle of 14 of violin includes the red and the green region too. So each red region is counted twice and the green region is counted 3 times. Attachment:
Ques2.jpg [ 14.89 KiB  Viewed 4897 times ]
So 35  20 = 15 15  3 = 12 (Subtract once the triple counted green region. Now everything is double counted) 12/2 = 6 = Total number of people who play 2 or 3 instruments.
_________________
Karishma Veritas Prep  GMAT Instructor My Blog
Get started with Veritas Prep GMAT On Demand for $199
Veritas Prep Reviews



Intern
Joined: 29 Aug 2011
Posts: 23

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
05 Feb 2012, 02:18
slingfox wrote: Of a group of people, 10 play piano, 11 play guitar, 14 play violin, 3 play all the instruments, 20 play only one instrument. How many play 2 instruments?
A. 3 B. 6 C. 9 D. 12 E. 15 Total folks = 10 + 11 + 14 = 35 20 Play only one instrument. So no of people playing two or more instruments = 35  20 = 15. From the venn diagrams we know that 15 represents the intersection part between Piano, Guitar and Violin. In the venn diagram, people having all the three capabilities are counted thrice. Hence people playing exactly two instruments = 15  3 (3) = 6 Hence B. Direct formulas may not be applicable all the time. Focus on which area is being counted and how many times.



Manager
Joined: 31 Jan 2012
Posts: 74

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
05 Feb 2012, 02:47
The way I did it was add up all the instruments together, so 10 + 11 +14 = 35. I knew 3 people played all 3, so I subtract 3 from each of the instruments, so 7+8+11 = 26. I know this is the amount of instruments played by a person who plays 1 or 2 instruments. Since the amount of people that play 1 instrument is 20, you subtract all the single instrument from the total. 2620=6, so 6 instrument. We know that people in this group play 2 instruments, so there is 3 people playing 6 instruments. 3 people who plays exactly 2 instruments + 3 people who plays exactly 3 = 6 people who play 2 or more instruments.



Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 176
Location: India
Concentration: Finance, International Business
WE: Information Technology (Investment Banking)

Re: Overlapping Sets Problem [#permalink]
Show Tags
05 Feb 2012, 03:19
VeritasPrepKarishma wrote: MBAhereIcome wrote: those who play single instrument = 20 those who don't play a single instrument (play 2 or 3) = 3520 = 15
those who play 2 instruments = 153 = 12 (3 play all three instruments) The 35 that you counted: 10 + 11 + 14 double counts the number of people who play only 2 instruments and triple counts the number of people who play all 3 instruments. The circle of 10 of piano includes the red and the green region. The circle of 11 of Guitar includes the red and green region too. Similarly, the circle of 14 of violin includes the red and the green region too. So each red region is counted twice and the green region is counted 3 times. Attachment: Ques2.jpg So 35  20 = 15 15  3 = 12 (Subtract once the triple counted green region. Now everything is double counted) 12/2 = 6 = Total number of people who play 2 or 3 instruments. Hi, Dont you think the answer should be A i.e. 3 since the question asks for how many people who play 2 instruments and not atleast 2 instruments.



Math Expert
Joined: 02 Sep 2009
Posts: 39660

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
05 Feb 2012, 03:47
slingfox wrote: Of a group of people, 10 play piano, 11 play guitar, 14 play violin, 3 play all the instruments, 20 play only one instrument. How many play 2 instruments?
A. 3 B. 6 C. 9 D. 12 E. 15 To elaborate more. Look at the diagram below: Attachment:
Union_3sets.gif [ 11.63 KiB  Viewed 4791 times ]
To solve this question one should fundamentally understand two things: 1. What does the question ask: "How many play 2 instruments?" So, we should find the sum of the sectors 1, 2, 3, and 4. Notice that those who play two instruments include also those who play all three instruments, (sector 4); 2. What happens when we sum all three groups, 10 piano players, 11 guitar players and 14 violin players? When we add these three groups, we'll get 10+11+14=35 but some sections are counting more than once in this number: sections 1, 2, and 3 are counted twice and section 4 thrice. Now, if we subtract those who play only one instrument (inner white sections on the diagram), we'll get 3520=15, so twice sections 1, 2, and 3 plus thrice section 4 equals to 15. Since, 15 counts section 4, those who play all the instruments, thrice then of 153=12 counts these section twice. So, now 12 counts all sections 1, 2, 3 and 4 twice. We need to count them once thus divide this number by 2 > 12/2=6 play 2 instruments. Answer: B. Detailed analysis of this concept is here: formulaefor3overlappingsets69014.html#p729340subhajeet wrote: Hi, Dont you think the answer should be A i.e. 3 since the question asks for how many people who play 2 instruments and not atleast 2 instruments. No, if it were the case question would ask: "how many play EXACTLY 2 instruments?" How many play 2 instruments, means how many play at least 2 instruments, hence this group includes also those who play all 3 instruments. Refer to the link above for more on this issue. Hope it helps.
_________________
New to the Math Forum? Please read this: 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? Extrahard Quant Tests with Brilliant Analytics



Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 176
Location: India
Concentration: Finance, International Business
WE: Information Technology (Investment Banking)

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
06 Feb 2012, 02:20
Bunuel wrote: slingfox wrote: Of a group of people, 10 play piano, 11 play guitar, 14 play violin, 3 play all the instruments, 20 play only one instrument. How many play 2 instruments?
A. 3 B. 6 C. 9 D. 12 E. 15 To elaborate more. Look at the diagram below: Attachment: Union_3sets.gif To solve this question one should fundamentally understand two things: 1. What does the question ask: "How many play 2 instruments?" So, we should find the sum of the sectors 1, 2, 3, and 4. Notice that those who play two instruments include also those who play all three instruments, (sector 4); 2. What happens when we sum all three groups, 10 piano players, 11 guitar players and 14 violin players? When we add these three groups, we'll get 10+11+14=35 but some sections are counting more than once in this number: sections 1, 2, and 3 are counted twice and section 4 thrice. Now, if we subtract those who play only one instrument (inner white sections on the diagram), we'll get 3520=15, so twice sections 1, 2, and 3 plus thrice section 4 equals to 15. Since, 15 counts section 4, those who play all the instruments, thrice then of 153=12 counts these section twice. So, now 12 counts all sections 1, 2, 3 and 4 twice. We need to count them once thus divide this number by 2 > 12/2=6 play 2 instruments. Answer: B. Detailed analysis of this concept is here: formulaefor3overlappingsets69014.html#p729340subhajeet wrote: Hi, Dont you think the answer should be A i.e. 3 since the question asks for how many people who play 2 instruments and not atleast 2 instruments. No, if it were the case question would ask: "how many play EXACTLY 2 instruments?" How many play 2 instruments, means how many play at least 2 instruments, hence this group includes also those who play all 3 instruments. Refer to the link above for more on this issue. Hope it helps. Bunnel: Thanks for the explanation. But it becomes a bit confusing here. Looks like i have to extra vigilent for these type of statements.



Director
Joined: 24 Aug 2009
Posts: 503
Schools: Harvard, Columbia, Stern, Booth, LSB,

Of a group of people, 10 play piano, 11 play guitar [#permalink]
Show Tags
22 Aug 2012, 09:49
1
This post received KUDOS
Question wordings are very poor or at least very ambiguous. "How many play 2 instruments?" can be inferred in 2 ways (both of which are right) which creates unnecessary confusion 1) Play Exactly 2 instruments 2) Play at least 2 instruments
_________________
If you like my Question/Explanation or the contribution, Kindly appreciate by pressing KUDOS. Kudos always maximizes GMATCLUB worth Game Theory
If you have any question regarding my post, kindly pm me or else I won't be able to reply



Current Student
Status: Everyone is a leader. Just stop listening to others.
Joined: 22 Mar 2013
Posts: 961
Location: India
GPA: 3.51
WE: Information Technology (Computer Software)

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
15 Aug 2013, 14:58
Yes its language is not correct someone should edit it "how many play at least two instrument" or Change the OA to  A. I also got 3 when i saw 26% correct answers i thought its a tough problem but later i discovered this issue, which everyone else has also reported.
_________________
Piyush K
 Our greatest weakness lies in giving up. The most certain way to succeed is to try just one more time. ― Thomas A. Edison Don't forget to press> Kudos My Articles: 1. WOULD: when to use?  2. All GMATPrep RCs (New) Tip: Before exam a week earlier don't forget to exhaust all gmatprep problems specially for "sentence correction".



Senior Manager
Joined: 10 Jul 2013
Posts: 334

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
15 Aug 2013, 15:18
1
This post received KUDOS
slingfox wrote: Of a group of people, 10 play piano, 11 play guitar, 14 play violin, 3 play all the instruments, 20 play only one instrument. How many play 2 instruments?
A. 3 B. 6 C. 9 D. 12 E. 15 guitar = 11 piano = 10 violin = 14 1 or 2 instruments player = 103 +113 +143 = 359 = 26 1 instruments player = 20 so 2 instruments player = 2620 = 6 =B
_________________
Asif vai.....



Manager
Joined: 21 Aug 2012
Posts: 148

Re: Overlapping Sets Problem [#permalink]
Show Tags
15 Aug 2013, 20:05
VeritasPrepKarishma wrote: MBAhereIcome wrote: those who play single instrument = 20 those who don't play a single instrument (play 2 or 3) = 3520 = 15
those who play 2 instruments = 153 = 12 (3 play all three instruments) The 35 that you counted: 10 + 11 + 14 double counts the number of people who play only 2 instruments and triple counts the number of people who play all 3 instruments. The circle of 10 of piano includes the red and the green region. The circle of 11 of Guitar includes the red and green region too. Similarly, the circle of 14 of violin includes the red and the green region too. So each red region is counted twice and the green region is counted 3 times. Attachment: Ques2.jpg So 35  20 = 15 15  3 = 12 (Subtract once the triple counted green region. Now everything is double counted) 12/2 = 6 = Total number of people who play 2 or 3 instruments. The question only states that how many play 2 instruments. Nowhere it is mentioned that it asks for only 2 instruments or atleast 2 instruments???
_________________
MODULUS Concept > http://gmatclub.com/forum/inequalities158054.html#p1257636 HEXAGON Theory > http://gmatclub.com/forum/hexagontheorytipstosolveanyheaxgonquestion158189.html#p1258308



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7440
Location: Pune, India

Re: Overlapping Sets Problem [#permalink]
Show Tags
15 Aug 2013, 22:26
jaituteja wrote: VeritasPrepKarishma wrote: MBAhereIcome wrote: those who play single instrument = 20 those who don't play a single instrument (play 2 or 3) = 3520 = 15
those who play 2 instruments = 153 = 12 (3 play all three instruments) The 35 that you counted: 10 + 11 + 14 double counts the number of people who play only 2 instruments and triple counts the number of people who play all 3 instruments. The circle of 10 of piano includes the red and the green region. The circle of 11 of Guitar includes the red and green region too. Similarly, the circle of 14 of violin includes the red and the green region too. So each red region is counted twice and the green region is counted 3 times. Attachment: Ques2.jpg So 35  20 = 15 15  3 = 12 (Subtract once the triple counted green region. Now everything is double counted) 12/2 = 6 = Total number of people who play 2 or 3 instruments. The question only states that how many play 2 instruments. Nowhere it is mentioned that it asks for only 2 instruments or atleast 2 instruments??? I understand the confusion. But the language of sets is very mathematical and literal. Say, if I ask you, whether you play an instrument and you have to answer in yes or no, you will say yes even if you play 2/3/4 instruments. Similarly, if I ask you whether you play two instruments, you will answer yes even if you play 3/4 instruments. No of people who play two instruments includes number of people who play more than 2 too since these people certainly do play 2 instruments (and they play some more). If 'at least' or 'only' is mentioned, we will consider it accordingly.
_________________
Karishma Veritas Prep  GMAT Instructor My Blog
Get started with Veritas Prep GMAT On Demand for $199
Veritas Prep Reviews



Math Expert
Joined: 02 Sep 2009
Posts: 39660

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
16 Aug 2013, 01:57



Manager
Status: Persevering
Joined: 15 May 2013
Posts: 218
Location: India
Concentration: Technology, Leadership
GMAT Date: 08022013
GPA: 3.7
WE: Consulting (Consulting)

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
18 Aug 2013, 06:09
PiyushK wrote: Yes its language is not correct someone should edit it "how many play at least two instrument" or Change the OA to  A. I also got 3 when i saw 26% correct answers i thought its a tough problem but later i discovered this issue, which everyone else has also reported. The question never said exactly 2 instrument; had it done so your answer would have been correct, but the question said people who play two instrument which might include 3 people. hence the solution is exactly 2 once and all three once; 3+3=6
_________________
It's one thing to get defeated, but another to accept it.



Intern
Joined: 09 Jul 2013
Posts: 2

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
18 Aug 2013, 11:36
slingfox wrote: Of a group of people, 10 play piano, 11 play guitar, 14 play violin, 3 play all the instruments, 20 play only one instrument. How many play 2 instruments?
A. 3 B. 6 C. 9 D. 12 E. 15 play only piano 103=7 Play only guitar 113=8 Play only violin 143=11 so, 20=7+8+112overlapping set 2overlapping set=2620=6 so, the best answer is (B) Posted by Abdul Mannan Mian



Manager
Joined: 29 Aug 2013
Posts: 77
Location: United States
Concentration: Finance, International Business
GMAT 1: 590 Q41 V29 GMAT 2: 540 Q44 V20
GPA: 3.5
WE: Programming (Computer Software)

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
14 Sep 2013, 03:09
saxenaashi wrote: slingfox wrote: Of a group of people, 10 play piano, 11 play guitar, 14 play violin, 3 play all the instruments, 20 play only one instrument. How many play 2 instruments?
A. 3 B. 6 C. 9 D. 12 E. 15 Total folks = 10 + 11 + 14 = 35 20 Play only one instrument. So no of people playing two or more instruments = 35  20 = 15. From the venn diagrams we know that 15 represents the intersection part between Piano, Guitar and Violin. In the venn diagram, people having all the three capabilities are counted thrice. Hence people playing exactly two instruments = 15  3 (3) = 6 Hence B. Direct formulas may not be applicable all the time. Focus on which area is being counted and how many times. Here "6" that you have got is counted twice i.e. 2(Exactly two) = 6 Therefore 3 will be exactly two.. Hence if question asks 2 instruments then it will be Exactly 2 + All = 3 + 3 = 6 people..



Intern
Joined: 15 Sep 2013
Posts: 5

Re: Tough Overlapping Set Problem Veritas [#permalink]
Show Tags
20 Dec 2013, 09:15
35 TOTPeople  20 individual instr  3 ABC = 12 remain for 2 instr / 2 instr = ANS:6 people play 2



Intern
Joined: 10 Dec 2013
Posts: 20
Location: India
Concentration: Technology, Strategy
GPA: 3.9
WE: Consulting (Consulting)

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
05 Feb 2014, 11:24
Hi, I just used a very simple approach hope that might help some people who are trying to avoid cramming up the formula People playing all three instruments = 3 Now subtract this from each group to remove the common part for all 3 Piano(Two or one) = 7 Guitar(Two or one) = 8 Violin(Two or one) = 11 Now if we sum all of the above we will get the number of people who play either two or one instrument Sum(Two or one) = 26 Question tells us that there are 20 people who play exactly 1 instrument hence 2620 = 6 = People playing two instruments Hit Kudos if you found this helpful. Cheers and good luck



Intern
Joined: 14 Jan 2011
Posts: 27

Re: Of a group of people, 10 play piano, 11 play guitar, 14 play [#permalink]
Show Tags
24 Sep 2014, 08:36
Poorly written question,
if the question was how many people play at least 2 instruments than the answer would be 6
If the question was, as is implied by the majority of the answers, how many people played solely 2 instruments the answer would be 3.




Re: Of a group of people, 10 play piano, 11 play guitar, 14 play
[#permalink]
24 Sep 2014, 08:36



Go to page
Previous
1 2 3
Next
[ 46 posts ]




