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

 It is currently 17 Aug 2018, 19:59

### 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

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

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

Author Message
TAGS:

### Hide Tags

Intern
Joined: 21 Nov 2013
Posts: 12
If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

18 Dec 2013, 16:16
2
1
00:00

Difficulty:

5% (low)

Question Stats:

88% (00:53) correct 12% (00:58) wrong based on 113 sessions

### HideShow 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?

_________________

Any and all kudos are greatly appreciated. Thank you.

Magoosh GMAT Instructor
Joined: 28 Dec 2011
Posts: 4666
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

19 Dec 2013, 09:57
1
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:
http://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
_________________

Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Intern
Joined: 21 Nov 2013
Posts: 12
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

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”.
_________________

Any and all kudos are greatly appreciated. Thank you.

Intern
Joined: 22 Nov 2013
Posts: 3
Concentration: Nonprofit, Entrepreneurship
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

19 Dec 2013, 19:47
1
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.
Manager
Joined: 19 Apr 2013
Posts: 74
Concentration: Entrepreneurship, Finance
GMAT Date: 06-05-2015
GPA: 3.88
WE: Programming (Computer Software)
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

19 Dec 2013, 20:21
2
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

_________________

Thanks,
AB

+1 Kudos if you like and understand.

Intern
Joined: 21 Nov 2013
Posts: 12
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

20 Dec 2013, 11:44
@sjmarinov and @bhatiamanu05, both of those methods make sense. Appreciate the responses.
_________________

Any and all kudos are greatly appreciated. Thank you.

SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1835
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

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)

$$= \frac{5}{7} - \frac{2}{7}$$

$$= \frac{3}{7}$$

_________________

Kindly press "+1 Kudos" to appreciate

Non-Human User
Joined: 09 Sep 2013
Posts: 7749
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?  [#permalink]

### Show Tags

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.
_________________
Re: If the ratio of x to y is 2 to 5, then (y-x)/(x+y)? &nbs [#permalink] 28 Oct 2017, 04:02
Display posts from previous: Sort by

# Events & Promotions

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.