Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 25 Nov 2013
Posts: 15
Location: Italy

What is the ratio x : y: z ? [#permalink]
Show Tags
Updated on: 10 Jan 2014, 03:14
4
This post received KUDOS
11
This post was BOOKMARKED
Question Stats:
39% (01:05) correct 61% (01:07) wrong based on 220 sessions
HideShow timer Statistics
What is the ratio x : y: z ? (1) x + y = 2 z (2) 2x + 3y = z Hi all, I read here: http://www.manhattangmat.com/erratafdp5ed.cfmabout some mistakes in the guide of Manhattan GMAT FDPs, 5th edition. I focused my attention on the third one: "The answer to the question as written is (E). The question should stipulate that xyz > 0". This was the DS exercise: Solution: (1) INSUFFICIENT, because if you try to isolate x/y you get a variable expression. (2) the same (1)+(2) SUFFICIENT: x + y = 2z & 2x+ 3y = z so x+ y = 2(2*+ 3y) x + y = 4x + 6y and finally you get x/y = 5/(3) You can do the same to get y/z = 3 So you have x : y = 5/3 & y / z =3/1 > x : y : z = 5 : 3 : 1 Now, saying x:y = 1:2 or 2:4 is the same. In the same way, I can say x:y=1:2 or 1:2. So, given x : y : z = 5 : 3 : 1 we may have two variables positive and one negative, or two negative and one positive, but that doesn't matter, because we are interested in the ratio (that, if wholly multiplied by 1, doesn't change its meaning). In the Errata from the link I've posted, Manhattan GMAT team says that we must specify xyz > 0 , that means we must specify that we want the twovariablespositiveandonenegative case. But I believe is not necessary; in fact we do not care about the single variables, but about their ratio. In conclusion I think that the answer to this DS is C even without the condition xyz > 0. Someone can confirm me this? Thank you. Ric
Official Answer and Stats are available only to registered users. Register/ Login.
Originally posted by Ric123 on 09 Jan 2014, 21:57.
Last edited by Bunuel on 10 Jan 2014, 03:14, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to DS forum.





Math Expert
Joined: 02 Sep 2009
Posts: 44588

Re: What is the ratio x : y: z ? [#permalink]
Show Tags
10 Jan 2014, 03:17
2
This post received KUDOS
Expert's post
2
This post was BOOKMARKED
Ric123 wrote: What is the ratio x : y: z ? (1) x + y = 2 z (2) 2x + 3y = z Hi all, I read here: http://www.manhattangmat.com/erratafdp5ed.cfmabout some mistakes in the guide of Manhattan GMAT FDPs, 5th edition. I focused my attention on the third one: "The answer to the question as written is (E). The question should stipulate that xyz > 0". This was the DS exercise: Solution: (1) INSUFFICIENT, because if you try to isolate x/y you get a variable expression. (2) the same (1)+(2) SUFFICIENT: x + y = 2z & 2x+ 3y = z so x+ y = 2(2*+ 3y) x + y = 4x + 6y and finally you get x/y = 5/(3) You can do the same to get y/z = 3 So you have x : y = 5/3 & y / z =3/1 > x : y : z = 5 : 3 : 1 Now, saying x:y = 1:2 or 2:4 is the same. In the same way, I can say x:y=1:2 or 1:2. So, given x : y : z = 5 : 3 : 1 we may have two variables positive and one negative, or two negative and one positive, but that doesn't matter, because we are interested in the ratio (that, if wholly multiplied by 1, doesn't change its meaning). In the Errata from the link I've posted, Manhattan GMAT team says that we must specify xyz > 0 , that means we must specify that we want the twovariablespositiveandonenegative case. But I believe is not necessary; in fact we do not care about the single variables, but about their ratio. In conclusion I think that the answer to this DS is C even without the condition xyz > 0. Someone can confirm me this? Thank you. Ric We need xyz>0 condition to know that neither of the variables is 0. Notice that x=y=z=0, satisfy both statements and in this case x:y:z is undefined and not 5 : 3 : 1. Hope it's clear. P.S. Please read carefully and follow: rulesforpostingpleasereadthisbeforeposting133935.html Pay attention to the rules 2, 3, 7, and 10. Thank you.
_________________
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? Extrahard Quant Tests with Brilliant Analytics



Manager
Joined: 20 Dec 2013
Posts: 124

Re: What is the ratio x : y: z ? [#permalink]
Show Tags
10 Jan 2014, 05:48
1
This post received KUDOS
1
This post was BOOKMARKED
[quote="Ric123"]What is the ratio x : y: z ? (1) x + y = 2 z (2) 2x + 3y = z Statement I is insufficient: x = 1, y = 1, z = 1 x = 3, y = 5, z = 4 Statement II is insufficient using the same concept as the first one Combining is insufficient x + y = 2z 4x + 6y = 2z 4x + 6y = x + y 3x = 5y x = 5, y = 3, z = 1 x = 0, y = 0 z = 0 Hence E
_________________
76000 Subscribers, 7 million minutes of learning delivered and 5.6 million video views
Perfect Scores http://perfectscores.org http://www.youtube.com/perfectscores



Intern
Joined: 25 Nov 2013
Posts: 15
Location: Italy

Re: What is the ratio x : y: z ? [#permalink]
Show Tags
11 Jan 2014, 00:17
1
This post was BOOKMARKED
Bunuel wrote: Ric123 wrote: What is the ratio x : y: z ? (1) x + y = 2 z (2) 2x + 3y = z Hi all, I read here: http://www.manhattangmat.com/erratafdp5ed.cfmabout some mistakes in the guide of Manhattan GMAT FDPs, 5th edition. I focused my attention on the third one: "The answer to the question as written is (E). The question should stipulate that xyz > 0". This was the DS exercise: Solution: (1) INSUFFICIENT, because if you try to isolate x/y you get a variable expression. (2) the same (1)+(2) SUFFICIENT: x + y = 2z & 2x+ 3y = z so x+ y = 2(2*+ 3y) x + y = 4x + 6y and finally you get x/y = 5/(3) You can do the same to get y/z = 3 So you have x : y = 5/3 & y / z =3/1 > x : y : z = 5 : 3 : 1 Now, saying x:y = 1:2 or 2:4 is the same. In the same way, I can say x:y=1:2 or 1:2. So, given x : y : z = 5 : 3 : 1 we may have two variables positive and one negative, or two negative and one positive, but that doesn't matter, because we are interested in the ratio (that, if wholly multiplied by 1, doesn't change its meaning). In the Errata from the link I've posted, Manhattan GMAT team says that we must specify xyz > 0 , that means we must specify that we want the twovariablespositiveandonenegative case. But I believe is not necessary; in fact we do not care about the single variables, but about their ratio. In conclusion I think that the answer to this DS is C even without the condition xyz > 0. Someone can confirm me this? Thank you. Ric We need xyz>0 condition to know that neither of the variables is 0. Notice that x=y=z=0, satisfy both statements and in this case x:y:z is undefined and not 5 : 3 : 1. Hope it's clear. P.S. Please read carefully and follow: rulesforpostingpleasereadthisbeforeposting133935.html Pay attention to the rules 2, 3, 7, and 10. Thank you. Thank you, now it is clear. I read the rules, and I will follow them from now.



Manager
Joined: 17 Mar 2014
Posts: 69

Re: What is the ratio x : y: z ? [#permalink]
Show Tags
28 Jun 2014, 00:14
Ric123 wrote: What is the ratio x : y: z ? (1) x + y = 2 z (2) 2x + 3y = z Hi all, I read here: http://www.manhattangmat.com/erratafdp5ed.cfmabout some mistakes in the guide of Manhattan GMAT FDPs, 5th edition. I focused my attention on the third one: "The answer to the question as written is (E). The question should stipulate that xyz > 0". This was the DS exercise: Solution: (1) INSUFFICIENT, because if you try to isolate x/y you get a variable expression. (2) the same (1)+(2) SUFFICIENT: x + y = 2z & 2x+ 3y = z so x+ y = 2(2*+ 3y) x + y = 4x + 6y and finally you get x/y = 5/(3) You can do the same to get y/z = 3 So you have x : y = 5/3 & y / z =3/1 > x : y : z = 5 : 3 : 1 Now, saying x:y = 1:2 or 2:4 is the same. In the same way, I can say x:y=1:2 or 1:2. So, given x : y : z = 5 : 3 : 1 we may have two variables positive and one negative, or two negative and one positive, but that doesn't matter, because we are interested in the ratio (that, if wholly multiplied by 1, doesn't change its meaning). In the Errata from the link I've posted, Manhattan GMAT team says that we must specify xyz > 0 , that means we must specify that we want the twovariablespositiveandonenegative case. But I believe is not necessary; in fact we do not care about the single variables, but about their ratio. In conclusion I think that the answer to this DS is C even without the condition xyz > 0. Someone can confirm me this? Thank you. Ric Hey Ric, Can anyone tell me why MGMAT chose to go with xyz>0 instead of \(xyz\neq0\) Could \(xyx\neq0\)lead to answer being C or E ?



Intern
Joined: 25 Nov 2013
Posts: 15
Location: Italy

What is the ratio x : y: z ? [#permalink]
Show Tags
21 Aug 2014, 09:40
qlx wrote: Ric123 wrote: What is the ratio x : y: z ? (1) x + y = 2 z (2) 2x + 3y = z Hi all, I read here: http://www.manhattangmat.com/erratafdp5ed.cfmabout some mistakes in the guide of Manhattan GMAT FDPs, 5th edition. I focused my attention on the third one: "The answer to the question as written is (E). The question should stipulate that xyz > 0". This was the DS exercise: Solution: (1) INSUFFICIENT, because if you try to isolate x/y you get a variable expression. (2) the same (1)+(2) SUFFICIENT: x + y = 2z & 2x+ 3y = z so x+ y = 2(2*+ 3y) x + y = 4x + 6y and finally you get x/y = 5/(3) You can do the same to get y/z = 3 So you have x : y = 5/3 & y / z =3/1 > x : y : z = 5 : 3 : 1 Now, saying x:y = 1:2 or 2:4 is the same. In the same way, I can say x:y=1:2 or 1:2. So, given x : y : z = 5 : 3 : 1 we may have two variables positive and one negative, or two negative and one positive, but that doesn't matter, because we are interested in the ratio (that, if wholly multiplied by 1, doesn't change its meaning). In the Errata from the link I've posted, Manhattan GMAT team says that we must specify xyz > 0 , that means we must specify that we want the twovariablespositiveandonenegative case. But I believe is not necessary; in fact we do not care about the single variables, but about their ratio. In conclusion I think that the answer to this DS is C even without the condition xyz > 0. Someone can confirm me this? Thank you. Ric Hey Ric, Can anyone tell me why MGMAT chose to go with xyz>0 instead of \(xyz\neq0\) Could \(xyx\neq0\)lead to answer being C or E ? Hi qlx, As I wrote in the original post saying x:y=1:2 or x:y=1:2 is the same. So, stated x : y : z = 5 : 3 : 1, we know that the sign of y is different from the sign of x and z, but we do not know whether we have one positive variable and two negative ones, or the opposite. However, we do not need that information, because it does not impact the value of the ratio. xyz>0 tells us also that we are in the first case (two negative variables and one positive), but we didn't need to know that information to find the ratio. As Bunuel specified, we need to know only that none of them is zero. Note that xyz<0 would tell us that none of the variables is zero, and that one of them is negative (must be y). I think that xyz different from zero is enough to define the required ratio, leading to C answer, even if we can't say the signs of the three variables.



Retired Moderator
Status: I Declare War!!!
Joined: 02 Apr 2014
Posts: 243
Location: United States
Concentration: Finance, Economics
GMAT Date: 03182015
WE: Asset Management (Investment Banking)

Re: What is the ratio x : y: z ? [#permalink]
Show Tags
02 May 2015, 13:43
Hi, I straight away went to C Or E. in ext 5 seconds I sensed that 3 unknown, and two equations so came to E directly. Its a fluke that answer was correct. Please evaluate my approach. Thanks Celestial



Retired Moderator
Joined: 06 Jul 2014
Posts: 1266
Location: Ukraine
Concentration: Entrepreneurship, Technology
GMAT 1: 660 Q48 V33 GMAT 2: 740 Q50 V40

What is the ratio x : y: z ? [#permalink]
Show Tags
02 May 2015, 14:53
Celestial09 wrote: Hi, I straight away went to C Or E. in ext 5 seconds I sensed that 3 unknown, and two equations so came to E directly. Its a fluke that answer was correct. Please evaluate my approach. Thanks Celestial Hello Celestial09When you need to find exact values of these unknowns then it definetely E and your approach right. But in our case you should find only ratios and this is C. There is possible another trick when task asks about sum of two unknowns and sometimes it's possible to find even when we have three unknowns and two equations. In this types of tasks your approach is a pitfall. P.S. as was already said in this case was a typo about signs of this unknowns and this transform answer to the E
_________________
Simple way to always control time during the quant part. How to solve main idea questions without full understanding of RC. 660 (Q48, V33)  unpleasant surprise 740 (Q50, V40, IR3)  antidebrief



Senior Manager
Joined: 08 Dec 2015
Posts: 305

Re: What is the ratio x : y: z ? [#permalink]
Show Tags
14 Feb 2017, 13:24
People, is adding, subtracting the equations the right approach here? Isn't it used to find exact values for variables? Eliminate one var. and discover the other, plug in, solve, fine. But here we don't want exact values, so why are you manipulating the equations like this?..
Do I make myself clear? Thanks!



NonHuman User
Joined: 09 Sep 2013
Posts: 6641

Re: What is the ratio x : y: z ? [#permalink]
Show Tags
16 Mar 2018, 19:47
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




Re: What is the ratio x : y: z ?
[#permalink]
16 Mar 2018, 19:47






