Last visit was: 26 Apr 2026, 23:18 It is currently 26 Apr 2026, 23:18
Home
Messages
Tests
Schools
Events
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 (Easy)|   Algebra|      
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 26 Apr 2026
Posts: 109,921
Own Kudos:
811,475
 [3]
Given Kudos: 105,908
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,921
Kudos: 811,475
 [3]
If a - b = (a^2 - b^2)/(b^2 - a^2) and b^2 - a^2 ≠ 0, then b - a = 03 Sep 2021, 04:27
Kudos
Add Kudos
3
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:

76% (01:06) correct 24% (01:39) wrong based on 233 sessions

History

Date
Time
Result
Not Attempted Yet
If \(a - b = \frac{a^2 - b^2}{b^2 - a^2}\) and \(b^2 - a^2 ≠ 0\), then \(b - a =\)

A. -1
B. 0
C. 1
D. 2
E. It cannot be determined from the information given.
ShowHide Answer
Official Answer
C
User avatar
ash124
User avatar
Joined: 21 Jan 2018
Last visit: 06 Apr 2025
Posts: 107
Own Kudos:
88
 [1]
Given Kudos: 64
Status:Improving everyday
Location: India
Schools: ISB '23 Judge '23 Said '23 Sloan '24 Fuqua '24 LBS '24 CEIBS '24 INSEAD Jan 22 intake Yale '24
GMAT 1: 660 Q49 V31
GPA: 3.23
WE:Engineering (Aerospace and Defense)
Products:
My Reviews
Schools: ISB '23 Judge '23 Said '23 Sloan '24 Fuqua '24 LBS '24 CEIBS '24 INSEAD Jan 22 intake Yale '24
GMAT 1: 660 Q49 V31
Posts: 107
Kudos: 88
 [1]
If a - b = (a^2 - b^2)/(b^2 - a^2) and b^2 - a^2 ≠ 0, then b - a = 03 Sep 2021, 04:37
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
If \(a - b = \frac{a^2 - b^2}{b^2 - a^2}\) and \(b^2 - a^2 ≠ 0\), then \(b - a =\)

A. -1
B. 0
C. 1
D. 2
E. It cannot be determined from the information given.
Show more


Given:
a - b = (a^2 - b^2)/(b^2 - a^2)
b-a= ?

a-b = (a-b)(a+b)/(b-a)(b+a)

a-b = (a-b)/ -(a-b)

a-b = (a-b)/ -(a-b)
a - b = - 1
Be careful because b - a is asked

b-a =1

Answer C
avatar
oliviabrisbane
avatar
Joined: 01 Sep 2021
Last visit: 06 Sep 2021
Posts: 1
Given Kudos: 4
Location: United States
Schools: Booth '24 Stanford '24
Schools: Booth '24 Stanford '24
Posts: 1
Kudos: 0
If a - b = (a^2 - b^2)/(b^2 - a^2) and b^2 - a^2 ≠ 0, then b - a = 04 Sep 2021, 21:19
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hi,

For this problem, there is very little constraints on the numbers that a and b can be, only that b2-a2 does not equal zero.

Answer C works if they are consecutive numbers (a=2 and b=3) but it does not work if they are not (a=2 and b=5).

Am I thinking about this correctly? Do we not have to consider all possible forms of a and b?
User avatar
ash124
User avatar
Joined: 21 Jan 2018
Last visit: 06 Apr 2025
Posts: 107
Own Kudos:
88
Given Kudos: 64
Status:Improving everyday
Location: India
Schools: ISB '23 Judge '23 Said '23 Sloan '24 Fuqua '24 LBS '24 CEIBS '24 INSEAD Jan 22 intake Yale '24
GMAT 1: 660 Q49 V31
GPA: 3.23
WE:Engineering (Aerospace and Defense)
Products:
My Reviews
Schools: ISB '23 Judge '23 Said '23 Sloan '24 Fuqua '24 LBS '24 CEIBS '24 INSEAD Jan 22 intake Yale '24
GMAT 1: 660 Q49 V31
Posts: 107
Kudos: 88
If a - b = (a^2 - b^2)/(b^2 - a^2) and b^2 - a^2 ≠ 0, then b - a = 04 Sep 2021, 22:36
Kudos
Add Kudos
Bookmarks
Bookmark this Post
oliviabrisbane
Hi,

For this problem, there is very little constraints on the numbers that a and b can be, only that b2-a2 does not equal zero.

Answer C works if they are consecutive numbers (a=2 and b=3) but it does not work if they are not (a=2 and b=5).

Am I thinking about this correctly? Do we not have to consider all possible forms of a and b?
Show more

We need to consider one more expression
a - b = (a^2 - b^2)/(b^2 - a^2)
Note: This((a^2 - b^2)/(b^2 - a^2) ) will be -1 regardless of the values of a & b)

put a = 2 and b = 5 in it.

2- 5 = (4 - 25)/(25 - 4)
-3 = -1
not equal


In crux, numbers should fulfill two conditions
a - b = (a^2 - b^2)/(b^2 - a^2)
b^2 - a^2 ≠ 0
User avatar
chetan2u
User avatar
GMAT Expert
Joined: 02 Aug 2009
Last visit: 26 Apr 2026
Posts: 11,229
Own Kudos:
45,025
Given Kudos: 335
Status:Math and DI Expert
Location: India
Concentration: Human Resources, General Management
GMAT Focus 1: 735 Q90 V89 DI81
Products:
My Reviews
Expert
Expert reply
GMAT Focus 1: 735 Q90 V89 DI81
Posts: 11,229
Kudos: 45,025
If a - b = (a^2 - b^2)/(b^2 - a^2) and b^2 - a^2 ≠ 0, then b - a = 04 Sep 2021, 22:51
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
If \(a - b = \frac{a^2 - b^2}{b^2 - a^2}\) and \(b^2 - a^2 ≠ 0\), then \(b - a =\)

A. -1
B. 0
C. 1
D. 2
E. It cannot be determined from the information given.
Show more


\(a - b = \frac{a^2 - b^2}{b^2 - a^2}=\frac{(a-b)(a+b)}{(b-a)(b+a)}=\frac{a-b}{b-a}\)

a-b can be canceled out from two sides.

\(1=\frac{1}{b-a}\)

\(b-a=1\)


C
User avatar
Crytiocanalyst
User avatar
Joined: 16 Jun 2021
Last visit: 27 May 2023
Posts: 942
Own Kudos:
214
Given Kudos: 309
Posts: 942
Kudos: 214
If a - b = (a^2 - b^2)/(b^2 - a^2) and b^2 - a^2 ≠ 0, then b - a = 04 Sep 2021, 23:06
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
If \(a - b = \frac{a^2 - b^2}{b^2 - a^2}\) and \(b^2 - a^2 ≠ 0\), then \(b - a =\)

A. -1
B. 0
C. 1
D. 2
E. It cannot be determined from the information given.
Show more
a−b=a2−b2
=>(a−b)(a+b)/(b−a)(b+a)
=>a−b/b−a
=>-1
b-a =1
Therefore IMO C
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 38,990
Own Kudos:
1,118
Posts: 38,990
Kudos: 1,118
If a - b = (a^2 - b^2)/(b^2 - a^2) and b^2 - a^2 ≠ 0, then b - a = 18 May 2025, 05:38
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Automated notice from GMAT Club BumpBot:

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

This post was generated automatically.
Moderators:
Bunuel
Math Expert
109921 posts
Krunaal
Tuck School Moderator
852 posts