Last visit was: 20 Nov 2025, 06:29 It is currently 20 Nov 2025, 06:29
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
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
Back to Forum
Create Topic
505-555 Level|   Algebra|      
User avatar
vikasp99
User avatar
Joined: 02 Jan 2017
Last visit: 20 Nov 2025
Posts: 263
Own Kudos:
1,823
 [19]
Given Kudos: 236
Location: Canada
Posts: 263
Kudos: 1,823
 [19]
If 5x = 4y, which of the following is NOT true? Updated on: 27 Feb 2017, 17:37
Originally posted by vikasp99 on 26 Feb 2017, 19:31.
Last edited by mikemcgarry on 27 Feb 2017, 17:37, edited 1 time in total.
changed to proper fraction notation
1
Kudos
Add Kudos
18
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

15% (low)

Question Stats:

78% (01:29) correct 22% (01:47) wrong based on 607 sessions

History

Date
Time
Result
Not Attempted Yet
If 5x = 4y, which of the following is NOT true?

(A) \(\frac{(x + y)}{y} = \frac{9}{5}\)

(B) \(\frac{y}{(y – x)} = 5\)

(C) \(\frac{(x – y)}{y} = \frac{1}{5}\)

(D) \(\frac{4x}{5y} = \frac{16}{25}\)

(E) \(\frac{(x + 3y)}{x} = \frac{19}{4}\)
ShowHide Answer
Official Answer
C
Most Helpful Reply
User avatar
Abhishek009
User avatar
Board of Directors
Joined: 11 Jun 2011
Last visit: 18 Jul 2025
Posts: 5,934
Own Kudos:
5,329
 [5]
Given Kudos: 463
Status:QA & VA Forum Moderator
Location: India
GPA: 3.5
WE:Business Development (Commercial Banking)
Posts: 5,934
Kudos: 5,329
 [5]
If 5x = 4y, which of the following is NOT true? 28 Feb 2017, 09:38
4
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
vikasp99
If 5x = 4y, which of the following is NOT true?

(A) \(\frac{(x + y)}{y} = \frac{9}{5}\)

(B) \(\frac{y}{(y – x)} = 5\)

(C) \(\frac{(x – y)}{y} = \frac{1}{5}\)

(D) \(\frac{4x}{5y} = \frac{16}{25}\)

(E) \(\frac{(x + 3y)}{x} = \frac{19}{4}\)
Show more

5x = 4y = 20 (Say)

So, x = 4 & y = 5

(A) \(\frac{(x + y)}{y} = \frac{9}{5}\) ( True )

(B) \(\frac{y}{(y – x)} = 5\) ( True )

(C) \(\frac{(x – y)}{y} = \frac{-1}{5}\)

(D) \(\frac{4x}{5y} = \frac{16}{25}\) ( True )

(E) \(\frac{(x + 3y)}{x} = \frac{19}{4}\) ( True )

Thus, answer must be (C)
General Discussion
User avatar
mikemcgarry
User avatar
Magoosh GMAT Instructor
Joined: 28 Dec 2011
Last visit: 06 Aug 2018
Posts: 4,479
Own Kudos:
30,537
 [3]
Given Kudos: 130
Expert
Expert reply
Posts: 4,479
Kudos: 30,537
 [3]
If 5x = 4y, which of the following is NOT true? 27 Feb 2017, 17:44
3
Kudos
Add Kudos
Bookmarks
Bookmark this Post
vikasp99
If 5x = 4y, which of the following is NOT true?

(A) \(\frac{(x + y)}{y} = \frac{9}{5}\)

(B) \(\frac{y}{(y – x)} = 5\)

(C) \(\frac{(x – y)}{y} = \frac{1}{5}\)

(D) \(\frac{4x}{5y} = \frac{16}{25}\)

(E) \(\frac{(x + 3y)}{x} = \frac{19}{4}\)
Show more
Dear vikasp99,

I'm happy to respond. :-)

There are many different ways to rearrange a ratio. The way I solved this was to scan down the list of answers. I noticed that (B) and (C) are close to reciprocals for each other, but the subtraction is in a reverse order between them. They can't both work for the values of x and y!

Think about it this way. Suppose x and y are both positive--they don't have to be, because they both could be negative, but let's just assume that they are positive. Each expression has to work for all numbers, so it must work for positive numbers! We know 5/4 = y/x, so y is a bigger positive number than x. Thus, (y - x) is positive, and (x - y) is negative.

Choice (B) has positive = positive
Choice (C) has negative = positive, so this is the one that doesn't work.

Thus, (C) is the answer.

(A), (B) (D), and (E) are all arithmetically legal rearrangements of the original equation.

Does all this make sense?
Mike :-)
User avatar
BrentGMATPrepNow
User avatar
Major Poster
Joined: 12 Sep 2015
Last visit: 31 Oct 2025
Posts: 6,739
Own Kudos:
35,359
 [3]
Given Kudos: 799
Location: Canada
Expert
Expert reply
Posts: 6,739
Kudos: 35,359
 [3]
If 5x = 4y, which of the following is NOT true? 28 Feb 2017, 10:06
3
Kudos
Add Kudos
Bookmarks
Bookmark this Post
vikasp99
If 5x = 4y, which of the following is NOT true?

(A) \(\frac{(x + y)}{y} = \frac{9}{5}\)

(B) \(\frac{y}{(y – x)} = 5\)

(C) \(\frac{(x – y)}{y} = \frac{1}{5}\)

(D) \(\frac{4x}{5y} = \frac{16}{25}\)

(E) \(\frac{(x + 3y)}{x} = \frac{19}{4}\)
Show more

Another approach is to apply a nice (and often-tested) concept: \(\frac{a + b}{c} = \frac{a}{c} + \frac{b}{c}\)
For example: \(\frac{1 + 2}{5} = \frac{1}{5} + \frac{2}{5}\)

Given: 5x = 4y
Divide both sides by y to get: 5x/y = 4
Divide both sides by 5 to get: x/y = 4/5

Now let's examine each answer choice and apply the nice rule.
A) (x + y)/y = 9/5
(x + y)/y = x/y + y/y [here, we applied the above rule]
= x/y + 1
= 4/5 + 5/5
= 9/5
This checks out.

B) y/(y – x) = 5
In this case, the denominator is not a single expression, so we can't readily apply our rule.
So, let's IGNORE answer choice B for now.

C) (x – y)/y = 1/5
(x – y)/y = x/y - y/y [here, we applied the above rule]
= x/y - 1
= 4/5 - 5/5
= -1/5
No good!
Answer: C

Cheers,
Brent
User avatar
mimajit
User avatar
Joined: 03 Aug 2017
Last visit: 24 Jun 2020
Posts: 75
Own Kudos:
28
 [1]
Given Kudos: 85
Posts: 75
Kudos: 28
 [1]
If 5x = 4y, which of the following is NOT true? 22 Aug 2018, 00:29
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
vikasp99
If 5x = 4y, which of the following is NOT true?

(A) \(\frac{(x + y)}{y} = \frac{9}{5}\)

(B) \(\frac{y}{(y – x)} = 5\)

(C) \(\frac{(x – y)}{y} = \frac{1}{5}\)

(D) \(\frac{4x}{5y} = \frac{16}{25}\)

(E) \(\frac{(x + 3y)}{x} = \frac{19}{4}\)
Show more

This is how I solved

Assign values to X and Y such that

5x = 4y, Here we could assign X as 4 and Y = 5

Now cross check ans

(A) (x+y)/y =9/5
=( 4+5)/5 = 9/5 SO its true

Similarly

(B) y/(y–x) =5
= 5( 5-4 ) = 5* 1 = 5 its true

(C) (x–y)/y =1/5
(4-5)/5 = -1/5 which is not the same as 1/5 hence its not true .
Ans = C





=
User avatar
ScottTargetTestPrep
User avatar
Target Test Prep Representative
Joined: 14 Oct 2015
Last visit: 20 Nov 2025
Posts: 21,719
Own Kudos:
27,002
 [2]
Given Kudos: 300
Status:Founder & CEO
Affiliations: Target Test Prep
Location: United States (CA)
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 21,719
Kudos: 27,002
 [2]
If 5x = 4y, which of the following is NOT true? 18 Nov 2019, 09:46
1
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
vikasp99
If 5x = 4y, which of the following is NOT true?

(A) \(\frac{(x + y)}{y} = \frac{9}{5}\)

(B) \(\frac{y}{(y – x)} = 5\)

(C) \(\frac{(x – y)}{y} = \frac{1}{5}\)

(D) \(\frac{4x}{5y} = \frac{16}{25}\)

(E) \(\frac{(x + 3y)}{x} = \frac{19}{4}\)
Show more

Simplifying each answer choice, we have:

A)

5x + 5y = 9y

5x = 4y

A is true.

B)

y = 5y - 5x

5x = 4y

B is true.

C)

5x - 5y = y

5x = 6y

C is not true.

Alternate Solution:

One solution for 5x = 4y is x = 4 and y = 5. Let’s substitute x = 4 and y = 5 to the given expressions until we find one which is not true:

A)

(4 + 5)/5 = 9/5

A is true.

B)

5/(5 - 4) = 5

B is true.

C)

(4 - 5)/5 = -1/5 ≠ 1/5

C is not true.

Answer: C
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 38,598
Own Kudos:
1,079
Posts: 38,598
Kudos: 1,079
If 5x = 4y, which of the following is NOT true? 04 Sep 2025, 11:55
Kudos
Add Kudos
Bookmarks
Bookmark this Post
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.
Moderators:
Bunuel
Math Expert
105416 posts
Krunaal
Tuck School Moderator
805 posts