Last visit was: 11 Jul 2025, 01:45 It is currently 11 Jul 2025, 01:45
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
MHIKER
Joined: 14 Jul 2010
Last visit: 24 May 2021
Posts: 945
Own Kudos:
5,455
 [43]
Given Kudos: 690
Status:No dream is too large, no dreamer is too small
Concentration: Accounting
Posts: 945
Kudos: 5,455
 [43]
2
Kudos
Add Kudos
41
Bookmarks
Bookmark this Post
Most Helpful Reply
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 11 July 2025
Posts: 102,634
Own Kudos:
Given Kudos: 98,170
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 102,634
Kudos: 740,281
 [17]
7
Kudos
Add Kudos
10
Bookmarks
Bookmark this Post
User avatar
BrentGMATPrepNow
User avatar
Major Poster
Joined: 12 Sep 2015
Last visit: 13 May 2024
Posts: 6,755
Own Kudos:
34,056
 [6]
Given Kudos: 799
Location: Canada
Expert
Expert reply
Posts: 6,755
Kudos: 34,056
 [6]
4
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
General Discussion
User avatar
MathRevolution
User avatar
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Last visit: 27 Sep 2022
Posts: 10,078
Own Kudos:
18,733
 [1]
Given Kudos: 4
GMAT 1: 760 Q51 V42
GPA: 3.82
Expert
Expert reply
GMAT 1: 760 Q51 V42
Posts: 10,078
Kudos: 18,733
 [1]
Kudos
Add Kudos
1
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 independent equations ensures a solution.

If x and y are positive integers, what is the value of (x+y)^2

(1) x = y -3
(2) x and y are prime numbers.

There are 2 variables (x,y) and 2 equations are given by the conditions, so there is high chance (C) will become the answer.
Looking at the conditions together, only x=2, y=5 works, as only 2 works for even prime numbers, and even+odd=odd.
Hence, the answer becomes (C).

For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
avatar
santro789
Joined: 30 Apr 2013
Last visit: 22 Feb 2020
Posts: 58
Own Kudos:
Given Kudos: 9
Posts: 58
Kudos: 10
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I did understand the above but any other methods to solve this?
User avatar
Basshead
Joined: 09 Jan 2020
Last visit: 07 Feb 2024
Posts: 927
Own Kudos:
Given Kudos: 432
Location: United States
Posts: 927
Kudos: 287
Kudos
Add Kudos
Bookmarks
Bookmark this Post
If x and y are positive integers, what is the value of (x+y)^2?
What is the value of \(x^2 + 2xy + y^2\)?

(1) x = y -3

Clearly we can get different values. INSUFFICIENT.

(2) x and y are prime numbers.

Again, clearly INSUFFICIENT.

(1&2) If x = y - 3 and both x and y are prime, then we can conclude x = 2 and y = 5. SUFFICIENT.
User avatar
MHIKER
Joined: 14 Jul 2010
Last visit: 24 May 2021
Posts: 945
Own Kudos:
Given Kudos: 690
Status:No dream is too large, no dreamer is too small
Concentration: Accounting
Posts: 945
Kudos: 5,455
Kudos
Add Kudos
Bookmarks
Bookmark this Post
MHIKER
If x and y are positive integers, what is the value of (x+y)^2

(1) x = y -3
(2) x and y are prime numbers.


(1) \(x-y=-3;\) Lots values will give the result, such as; 2-5=-3, 4-7=-3, So, x (first value) and y (the second) value are different in the two cases. Insufficient.

(2) There are lots of primes numbers; Insufficient.

Considering both:
We know that \(Even -Odd=Odd\), There is only one even prime number and that is 2. So, x=2 and y=5, Sufficient.

The answer is \(C.\)
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 37,376
Own Kudos:
1,010
 [1]
Posts: 37,376
Kudos: 1,010
 [1]
1
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.
Moderator:
Math Expert
102634 posts