NEW HERE? LEARN MORE
closeclose
Last visit was: 29 Apr 2024, 08:15 It is currently 29 Apr 2024, 08:15
Decision Tracker
My Rewards
New posts
New comers' posts

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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
avatar
MrWallSt
Intern
Intern
Joined: 21 Nov 2013
Posts: 11
Own Kudos [?]: 72 [3]
Given Kudos: 9
Send PM
If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   18 Dec 2013, 16:16
2
Kudos
1
Bookmarks
00:00
A
B
C
D
E

Difficulty:

5% (low)

Question Stats:

93% (01:01) correct 7% (01:09) wrong based on 124 sessions
Hide Show timer Statistics
If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?

A. -7/3
B. -3/7
C. 3/7
D. 1
E. 7/3

Can any one solve this using algebra and not plugging in?
ShowHide Answer
Official Answer
C
User avatar
G
mikemcgarry
Magoosh GMAT Instructor
Joined: 28 Dec 2011
Posts: 4452
Own Kudos [?]: 28583 [1]
Given Kudos: 130
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   19 Dec 2013, 09:57
1
Kudos
Expert Reply
MrWallSt wrote:
If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?

A. -7/3
B. -3/7
C. 3/7
D. 1
E. 7/3

Can any one solve this using algebra and not plugging in?

Dear MrWallSt,
I'm happy to respond. :-)

With all due respect, I believe the short answer to your question is simply "no." This is a very straightforward question, very easy, designed as a simple plug-in question by the test author. Plugging in is the ideal way to approach this problem. I know lots of algebra, through multivariable calculus, and it's really somewhat beyond me what algebra one would use to approach this. I honestly think that no one skilled in mathematics would want to bring the machinery of algebra anywhere near this problem.

Your very question makes me suspicious. Yes, algebra is awfully useful in a large number of problems, but it is unreasonable to think that algebra can be used in every single problem. It is highly unfruitful to see the letter x and immediately leap to algebra: that is precisely the kind of trap that GMAT writers design to ensnare students! If you routinely think this way, that mindset is an addiction to algebra and this addiction definitely will drag down your GMAT Quant score if you don't manage it.

The GMAT Quant section will always keep you on your toes. There's nothing you can memorize, no fixed set of rules, that will give you success every day. As soon as the GMAT writers realize that a large number of test-takers are using one fixed approach, they start writing problems designed to frustrate folks who are too attached to their rigid method. If you can't maintain mental agility, the GMAT will punish you. Here's an article about the type of thinking the GMAT demands:
https://magoosh.com/gmat/2013/mathematic ... -the-gmat/

I hope this wasn't too emphatic a response. You may not be an "algebra addict" at all, but I have met many of them preparing for the GMAT, and I like to warn students of this danger.

I hope all this helps.
Mike :-)
avatar
MrWallSt
Intern
Intern
Joined: 21 Nov 2013
Posts: 11
Own Kudos [?]: 72 [0]
Given Kudos: 9
Send PM
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   19 Dec 2013, 12:24
Thank you very much for your response. I am huge fan of your math and sentence correction blogs. I will say that my tendency to revert to algebra is something that I most certainly need to work on. In this case, I was able to solve the problem using plugging in numbers. However, since ratios (along with coordinate geometry, divisibility, inequalities and odds/evens) is something that I need to develop, I thought that being able to follow an algebraic solution would help my understanding of ratios in general. If this is something that can not be solved / is too difficult to solve algebraically, it makes feel a little bit better. I have been working on having a better understanding of how to solve ratios conceptually and then saw this and thought “I have no idea how to solve this and guess it’s back to the basics”.
avatar
sjmarinov
Intern
Intern
Joined: 22 Nov 2013
Posts: 3
Own Kudos [?]: 6 [1]
Given Kudos: 84
Concentration: Nonprofit, Entrepreneurship
Send PM
GMAT ToolKit User
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   19 Dec 2013, 19:47
1
Kudos
I believe this problem can be solved using algebra.

The ratio of x to y is 2 to 5 means
(x/y)=(2/5)

Cross-multiply

2x = 5y
x = (2/5)*y

Then, substitute x in the original equation in the problem with the value we just found.

(y - (2/5)*y) / ((2/5)*y + y)
= ((3/5)*y) / ((7/5)*y)

Simplify by canceling the y in the numerator with the y in the denominator.
(3/5) / (7/5)
= (3/5) * (5/7)

The 5s cancel each other out, and you are left with 3/7.

I would love an expert to double check me on this, but this should be a sufficient way to complete the problem using algebra. However, plugging in numbers, in this case, is a more efficient way to complete the problem and is also less prone to error because you are eliminating variables.
User avatar
bhatiamanu05
Manager
Manager
Joined: 19 Apr 2013
Posts: 55
Own Kudos [?]: 186 [2]
Given Kudos: 9
Concentration: Entrepreneurship, Finance
GMAT Date: 06-05-2015
GPA: 3.88
WE:Programming (Computer Software)
Send PM
GMAT ToolKit User
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   19 Dec 2013, 20:21
2
Kudos
MrWallSt wrote:
If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?

A. -7/3
B. -3/7
C. 3/7
D. 1
E. 7/3

Can any one solve this using algebra and not plugging in?


In my point of view this is very easy question. You can use Componendo and dividendo method to reach the answer.

x/y= 2/5
x+y/x-y = 2+5/2-5
x+y/x-y = 7/-3
Can be written as -3/7 = x-y/x+y
also 3/7 = y-x/x+y


Thanks,
AB

+1 Kudos if you like and understand
avatar
MrWallSt
Intern
Intern
Joined: 21 Nov 2013
Posts: 11
Own Kudos [?]: 72 [0]
Given Kudos: 9
Send PM
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   20 Dec 2013, 11:44
@sjmarinov and @bhatiamanu05, both of those methods make sense. Appreciate the responses.
avatar
PareshGmat
SVP
SVP
Joined: 27 Dec 2012
Status:The Best Or Nothing
Posts: 1562
Own Kudos [?]: 7212 [0]
Given Kudos: 193
Location: India
Concentration: General Management, Technology
WE:Information Technology (Computer Software)
Send PM
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   02 Jul 2014, 01:31
\(\frac{x}{y} = \frac{2}{5}\)

We require to find \(\frac{y-x}{x+y} = \frac{y}{x+y} - \frac{x}{x+y}\)

\(\frac{y}{x} = \frac{5}{2}\)

\(\frac{y}{x+y} = \frac{5}{5+2} = \frac{5}{7}\) ......... (a)

\(\frac{x}{x+y} = \frac{2}{5+2} = \frac{2}{7}\) .......... (b)

(a) - (b)

\(= \frac{5}{7} - \frac{2}{7}\)

\(= \frac{3}{7}\)

Answer = C
User avatar
bumpbot
Non-Human User
Joined: 09 Sep 2013
Posts: 32736
Own Kudos [?]: 822 [0]
Given Kudos: 0
Send PM
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink] New post   28 Oct 2017, 04:02
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
gmatclubot
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? [#permalink]
28 Oct 2017, 04:02
Moderators:
Bunuel
Math Expert
93007 posts
yashikaaggarwal
Senior Moderator - Masters Forum
3137 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions