Last visit was: 25 Apr 2026, 21:26 It is currently 25 Apr 2026, 21:26
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.
Close
Request Expert Reply
Confirm Cancel
User avatar
atalpanditgmat
Joined: 02 Oct 2012
Last visit: 15 Nov 2013
Posts: 68
Own Kudos:
711
 [16]
Given Kudos: 23
Status:Working hard to score better on GMAT
Location: Nepal
Concentration: Finance, Entrepreneurship
GPA: 3.83
WE:Accounting (Consulting)
Posts: 68
Kudos: 711
 [16]
2
Kudos
Add Kudos
14
Bookmarks
Bookmark this Post
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 25 Apr 2026
Posts: 109,830
Own Kudos:
811,297
 [3]
Given Kudos: 105,886
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,830
Kudos: 811,297
 [3]
3
Kudos
Add Kudos
Bookmarks
Bookmark this Post
avatar
bugzor
Joined: 15 Sep 2012
Last visit: 09 Nov 2013
Posts: 7
Own Kudos:
4
 [2]
Given Kudos: 36
Posts: 7
Kudos: 4
 [2]
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 25 Apr 2026
Posts: 109,830
Own Kudos:
Given Kudos: 105,886
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,830
Kudos: 811,297
Kudos
Add Kudos
Bookmarks
Bookmark this Post
bugzor
I arrived at B as well, atalpanditgmat can you please correct the OA

OA edited. Thank you.
avatar
deepthij
Joined: 26 Oct 2014
Last visit: 24 Dec 2016
Posts: 6
Own Kudos:
Given Kudos: 7
Posts: 6
Kudos: 1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
bugzor
I arrived at B as well, atalpanditgmat can you please correct the OA

OA edited. Thank you.

Hi,

From Statement 1 , a + b = 5 is obtained right. Why is it insufficient then? Pls help.
User avatar
MathRevolution
User avatar
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Last visit: 27 Sep 2022
Posts: 10,063
Own Kudos:
Given Kudos: 4
GMAT 1: 760 Q51 V42
GPA: 3.82
Expert
Expert reply
GMAT 1: 760 Q51 V42
Posts: 10,063
Kudos: 20,005
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Forget conventional ways of solving math questions. In DS, Variable approach is

the easiest and quickest way to find the answer without actually solving the

problem. Remember equal number of variables and equations ensures a solution.


If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what is the value of a + b?

(1) ax^2 = a
(2) bx^3 = b

Transforming the original condition and the question we have 3 variables (a,b,x) and 1 equation (ax^2 + bx^3 = 5). Since we need to match the number of variables and equations,we need 2 more, therefore C is likely the answer. Using both 1) & 2) together, ax^2 + bx^3 = 5--> a+b=5 thus the answer is C. However, this is a 'trivial' case and thus is not our answer. Therefore using common mistake type 4(A),
1) ax^2=a--> x=-1,1. Substituting x=-1 to ax^2+bx^3=5 we have a-b=5 thus a=6, b=1 or a=7, b=2. Our answer is a+b=7,9..etc which is not unique and therefore not sufficient.
2) bx^3=b --> b=1, thus substituting it inside ax^2 + bx^3 = 5 gives us a+b=5. the answer is unique, therefore the answer is B.
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 25 Apr 2026
Posts: 109,830
Own Kudos:
811,297
 [1]
Given Kudos: 105,886
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,830
Kudos: 811,297
 [1]
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
deepthij
Bunuel
bugzor
I arrived at B as well, atalpanditgmat can you please correct the OA

OA edited. Thank you.

Hi,

From Statement 1 , a + b = 5 is obtained right. Why is it insufficient then? Pls help.

From (1) we have that IF x = 1, then a + b = 5, but IF x = -1, then a - b = 5. Now, if x = -1, then from a - b = 5 we cannot say whether a + b = 5.
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 38,986
Own Kudos:
Posts: 38,986
Kudos: 1,118
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:
Math Expert
109830 posts
498 posts
212 posts