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

It is currently 02 Oct 2014, 05:22

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

What is the value of x + y?

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
1 KUDOS received
Intern
Intern
avatar
Joined: 02 Apr 2013
Posts: 4
GMAT 1: 570 Q47 V28
Followers: 0

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

What is the value of x + y? [#permalink] New post 02 Apr 2013, 09:05
1
This post received
KUDOS
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

52% (01:46) correct 48% (00:53) wrong based on 48 sessions
What is the value of x + y?

(1) xy = 24
(2) x/y = 8/3

[Reveal] Spoiler:
OA is E.

i understand why it can't be A, B or D but i am having problems to figure out why it would not be "C". i would say, with the information given by (1) AND (2) the values for x = 8 and y = 3, which fits both indications. am i missing something about the perspective if some of the values (or both?!) are negative? i just don't get it.

thx for a reply!
[Reveal] Spoiler: OA

Last edited by Bunuel on 02 Apr 2013, 09:08, edited 1 time in total.
Edited the question.
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23079
Followers: 3544

Kudos [?]: 27359 [0], given: 2734

Re: What is the value of x + y? [#permalink] New post 02 Apr 2013, 09:13
Expert's post
What is the value of x + y?

(1) xy = 24
(2) x/y = 8/3

Each statement alone is clearly insufficient.

(1)+(2) From (2) we have that x=\frac{8y}{3}, thus from (1) xy =\frac{8y}{3}*y =24 --> y^2=9 --> y=3 or y=-3. If y=3, then x=8 and x+y=11 but if y=-3, then x=-8 and x+y=-11. Two different answers, hence insufficient.

Answer: E.

Hope it's clear.
_________________

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

Expert Post
3 KUDOS received
Veritas Prep GMAT Instructor
User avatar
Joined: 11 Dec 2012
Posts: 313
Followers: 59

Kudos [?]: 190 [3] , given: 66

Re: What is the value of x + y? [#permalink] New post 02 Apr 2013, 10:13
3
This post received
KUDOS
Expert's post
Bunuel wrote:
What is the value of x + y?

(1) xy = 24
(2) x/y = 8/3

Each statement alone is clearly insufficient.

(1)+(2) From (2) we have that x=\frac{8y}{3}, thus from (1) xy =\frac{8y}{3}*y =24 --> y^2=9 --> y=3 or y=-3. If y=3, then x=8 and x+y=11 but if y=-3, then x=-8 and x+y=-11. Two different answers, hence insufficient.

Answer: E.

Hope it's clear.


Hi gmatfeelizzle, Bunuel's explanation above is correct, as always. Of course, on data sufficiency questions such as these, there are always three traps you must be mindful of. These traps show up in all kinds of DS questions and therefore should always be considered, even if they can be quickly disregarded in many questions.

The first trap is non-integer. It's easy to say that x*y = 24 must be 1-24, 2-12, 3-8 or 4-6, but it could just as easily be 1.5 and 16. Be wary of choices that don't have to be integers, which is the default case in math
The second trap is negatives. This is exactly where this question gets you. X/Y = 8/3 means that X is 8 and Y is 3... unless X is -8 and Y is -3, in which case you'll get the exact same value.
The third trap is zero. This number shows up all the time in data sufficiency and must be considered whenever you have data sufficiency questions. It is probably the most common trap used by the GMAT. It is especially common if the question is asking about positive or negative numbers, multiples or the keyword nonnegative. If you see nonnegative, immediately consider 0.

In this case the trap was negatives, but these three possibilities are the trinity of traps (or trapnity?).

Hope this helps!
-Ron
_________________

Ron Awad
Veritas Prep | GMAT Instructor
Save $100 on Veritas Prep GMAT Courses and Admissions Consulting Services
Veritas Prep Reviews

1 KUDOS received
Intern
Intern
User avatar
Status: Currently Preparing the GMAT
Joined: 15 Feb 2013
Posts: 31
Location: United States
GMAT 1: 550 Q47 V23
GPA: 3.7
WE: Analyst (Consulting)
Followers: 1

Kudos [?]: 4 [1] , given: 11

Re: What is the value of x + y? [#permalink] New post 02 Apr 2013, 14:09
1
This post received
KUDOS
Great post gmatfeelizzle and we'll gladly help you out with your query. So let's get started :

We are looking for the value of x + y.
Now in value-based DS question, you should expect to get one and only one value per question. If, when solving the question, you stumble on two distinct values, then the answer will most likely be E.

Statement 1 :x*y = 24
This statement alone is insufficient because we can think of a multitude of possibilities for both x and y that yield the result given (24) but when plugged into x + y, it will yield different results. For instance :
x = 4 and y = 6 =>x + y = 10
x = 3 and y = 8 =>x + y = 11
And so on. You should also think about negative integers as well (since the DS question stem doesn't seem to indicate any signum constraint on the variables we're manipulating).

Statement 2 : \frac{x}{y} =\frac{8}{3}
Again the statement alone is insufficient for the same reasons as statement 1. We can think of many values for x and y that yield 8/3 but when plugged into x + y, it will yield different results.

Let's combine (1) and (2).

From 2 we get : x = \frac{8}{3}*y
Substituting in 1 yields : x*y = 24=> \frac{8}{3}*y*y = 24 => y^2 = 24*\frac{3}{8} => y^2 = 9
At this point, you are tempted to say thaty = 3, but since we have no signum constraints on the variables in hand, y can be 3 just as it can be -3.

Remember that even powers hide the base's sign !!!

So if y = 3, then x = \frac{8}{3}*y = 8. Yielding : x + y = 11
If y = -3, however, then x = \frac{8}{3}*y = -8. Yielding : x + y = -11

So even when combining the two statements, you get different results !! And that clashes with the basic outcome of a value-based DS question : if the question is solvable, then the value is unique ! Otherwise, the answer will almost always be E.

Which is actually the case in this question.

The answer was deliberately lengthy so as to answer your query about why "C" isn't the right answer.

Hope that helped. :-D
Intern
Intern
avatar
Joined: 02 Apr 2013
Posts: 4
GMAT 1: 570 Q47 V28
Followers: 0

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

Re: What is the value of x + y? [#permalink] New post 03 Apr 2013, 04:47
thank you guys for all your answers!

right, i made the mistake overseeing that the absolute value of (-8)/(-3) is just the same as the absolute value of 8/3, which made me pick answer choice C too quickly.

i really am impressed how fast and precisley your answers helped me to figure out where i was wrong! looking forward for some more tricky questions to discuss with you :-)

just one more question: do you think this question is correctly classified as a 600 - 700 questions or is it rather a below 600 one?
Intern
Intern
User avatar
Status: Currently Preparing the GMAT
Joined: 15 Feb 2013
Posts: 31
Location: United States
GMAT 1: 550 Q47 V23
GPA: 3.7
WE: Analyst (Consulting)
Followers: 1

Kudos [?]: 4 [0], given: 11

Re: What is the value of x + y? [#permalink] New post 03 Apr 2013, 11:20
gmatfeelizzle wrote:
just one more question: do you think this question is correctly classified as a 600 - 700 questions or is it rather a below 600 one?


This is most likely a sub-600 question. But that's just my opinion... :?
Re: What is the value of x + y?   [#permalink] 03 Apr 2013, 11:20
    Similar topics Author Replies Last post
Similar
Topics:
1 Experts publish their posts in the topic What is the value of x - y? registerincog 1 18 Nov 2013, 06:25
2 Experts publish their posts in the topic What is value of x - y? BukrsGmat 6 06 Apr 2013, 10:04
Experts publish their posts in the topic What is the value of x – y ? macjas 1 27 May 2012, 08:11
what is the value of x y nick_sun 9 11 Jun 2007, 06:03
What is the value of x-y? americo 2 29 May 2007, 05:19
Display posts from previous: Sort by

What is the value of x + y?

  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®.