Find all School-related info fast with the new School-Specific MBA Forum

It is currently 23 Jul 2014, 00:35

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If x and y are positive integers and 1 + x + y + xy = 15, wh

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
User avatar
Joined: 06 Apr 2010
Posts: 144
Followers: 3

Kudos [?]: 52 [0], given: 12

GMAT Tests User Reviews Badge
If x and y are positive integers and 1 + x + y + xy = 15, wh [#permalink] New post 12 Sep 2010, 06:15
00:00
A
B
C
D
E

Difficulty:

  25% (low)

Question Stats:

79% (02:02) correct 21% (01:43) wrong based on 39 sessions
If x and y are positive integers and 1 + x + y + xy = 15, what is the value of x + y?

A. 3
B. 5
C. 6
D. 8
E. 9
[Reveal] Spoiler: OA
Intern
Intern
avatar
Joined: 15 Aug 2010
Posts: 2
Followers: 0

Kudos [?]: 1 [0], given: 0

GMAT Tests User
Re: Arithmatic Problem [#permalink] New post 12 Sep 2010, 06:58
I think this is how it is calculated;

Factors of 15 are 1,3,5,and 15.

So 1 + x + y +xy = (1+x)(1+y) = 15. Basically find product of two numbers that is equal to 15. This can be factorized as follows

1 + x = 3 and 1 + y = 5 (as product of 3x5 = 15)
-> x = 2 and y = 4

OR

1 + x = 15 and 1 + y = 1 (as product of 15x1 = 15)
-> x=14 and y=0

However problem indicates that x,y>0, so value of x = 2 and y = 4.

Value of x+y = 2+4 = 6

Ans C
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18684
Followers: 3232

Kudos [?]: 22231 [0], given: 2601

Re: Arithmatic Problem [#permalink] New post 12 Sep 2010, 08:11
Expert's post
udaymathapati wrote:
What's the approach to solve following example.
If x and y are positive integers and 1 + x + y + xy = 15, what is the value of x + y?
A. 3
B. 5
C. 6
D. 8
E. 9


1+x+y+xy=15 --> (x+1)(y+1)=15=3*5;

As x and y are positive integers then x+1=3 and y+1=5, or vise-versa (x+1=1 and y+=15 or vise-versa is not possible as in this case one of the unknowns becomes zero and we are told that both unknowns are positive).

So x+1=3 and y+1=5, or vise-versa --> no need to solve for x and y, just add them --> x+1+y+1=3+5 --> x+y=6.

Answer: C.

_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Senior Manager
Senior Manager
avatar
Joined: 20 Jul 2010
Posts: 271
Followers: 2

Kudos [?]: 37 [0], given: 9

GMAT ToolKit User Reviews Badge
Re: Arithmatic Problem [#permalink] New post 12 Sep 2010, 08:26
I went by answe choices.
x+y+xy=14 (given)
If x+y = 3 then x=1, y 2 = cannot satisfy 14.
If x+y=5, x=4, y=1 cannot satisfy 14. x=2 and y=3 ..ruled out
x+y=6 = I got the answer

I liked the equation approach as its clean. Although I could solve it in less than a minute

_________________

If you like my post, consider giving me some KUDOS !!!!! Like you I need them

Re: Arithmatic Problem   [#permalink] 12 Sep 2010, 08:26
    Similar topics Author Replies Last post
Similar
Topics:
1 Experts publish their posts in the topic In the fraction x/y, where x and y are positive integers, wh Bunuel 4 28 Feb 2014, 03:04
2 Experts publish their posts in the topic In the fraction x/y, where x and y are positive integers, wh enigma123 16 29 Jan 2012, 15:58
Experts publish their posts in the topic In the fraction x/y, where x and y are positive integers, wh burnttwinky 8 21 Apr 2010, 18:17
2 In the fraction x/y, where x and y are positive integers, wh arjunrampal 6 29 Dec 2009, 09:26
If x and y are positive integers and 1 + x + y + xy = 15, topkool 3 01 Dec 2006, 06:26
Display posts from previous: Sort by

If x and y are positive integers and 1 + x + y + xy = 15, wh

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.