Summer is Coming! Join the Game of Timers Competition to Win Epic Prizes. Registration is Open. Game starts Mon July 1st.

It is currently 16 Jul 2019, 13:39

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

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

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Senior Manager
Senior Manager
User avatar
S
Status: No dream is too large, no dreamer is too small
Joined: 14 Jul 2010
Posts: 491
If x and y are positive integers, what is the value of (x+y)  [#permalink]

Show Tags

New post 22 Jan 2012, 08:20
15
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

71% (01:29) correct 29% (01:28) wrong based on 351 sessions

HideShow timer Statistics


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.

_________________
Most Helpful Expert Reply
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 56244
Re: what is the value of (x+y)^2  [#permalink]

Show Tags

New post 22 Jan 2012, 08:31
2
5
Baten80 wrote:
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.

I solved plugging number with trial error. Is there any short method?


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

(1) x = y-3. Clearly insufficient. Just notice from this statement that x<y.
(2) x and y are prime numbers. Also insufficient.

(1)+(2) As x<y and both are primes, y is some prime more than 2, so odd. Now, x={odd}-3={even} and as the only even prime is 2 then x=2 and y=5. Sufficient.

Answer: C.

Hope it's clear.
_________________
General Discussion
CEO
CEO
User avatar
V
Joined: 12 Sep 2015
Posts: 3847
Location: Canada
Re: If x and y are positive integers, what is the value of (x+y)  [#permalink]

Show Tags

New post 05 Dec 2015, 12:43
3
1
1
Baten80 wrote:
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.


Target question: What is the value of (x+y)²?

Given: x and y are positive integers

Statement 1: x = y - 3
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of x and y that satisfy statement 1. Here are two:
Case a: x = 1 and y = 4, in which case (x+y)² = (1+4)² = 5² = 25
Case b: x = 2 and y = 5, in which case (x+y)² = (2+5)² = 7² = 49
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, you can read my article: http://www.gmatprepnow.com/articles/dat ... lug-values

Statement 2: x and y are prime numbers
This statement doesn't FEEL sufficient either, so I'll TEST some values.
There are several values of x and y that satisfy statement 2. Here are two:
Case a: x = 2 and y = 2, in which case (x+y)² = (2+2)² = 4² = 16
Case b: x = 2 and y = 3, in which case (x+y)² = (2+3)² = 5² = 25
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that x = y - 3
In other words, x + 3 = y
Or we can say that x + ODD = y
This means that one of the two values (x or y) is EVEN and one is ODD

Statement 2 tells us that x and y are prime numbers
If one of the values is EVEN and also PRIME, then one value must equal 2.
Since x is smaller than y, we can conclude that x = 2, which means y = 5
Now that we know the values of x and y, we can see that (x+y)² = (2+5)² = 7² = 49

Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

Cheers,
Brent
_________________
Test confidently with gmatprepnow.com
Image
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 7590
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: If x and y are positive integers, what is the value of (x+y)  [#permalink]

Show Tags

New post 06 Dec 2015, 11:37
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.
_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Manager
Manager
avatar
B
Joined: 30 Apr 2013
Posts: 77
Re: If x and y are positive integers, what is the value of (x+y)  [#permalink]

Show Tags

New post 05 Sep 2017, 01:34
I did understand the above but any other methods to solve this?
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 11659
Re: If x and y are positive integers, what is the value of (x+y)  [#permalink]

Show Tags

New post 19 Sep 2018, 12:08
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.
_________________
GMAT Club Bot
Re: If x and y are positive integers, what is the value of (x+y)   [#permalink] 19 Sep 2018, 12:08
Display posts from previous: Sort by

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

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne