GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 21 Feb 2019, 14:44

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
Events & Promotions in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
  • Online GMAT boot camp for FREE

     February 21, 2019

     February 21, 2019

     10:00 PM PST

     11:00 PM PST

    Kick off your 2019 GMAT prep with a free 7-day boot camp that includes free online lessons, webinars, and a full GMAT course access. Limited for the first 99 registrants! Feb. 21st until the 27th.
  • Free GMAT RC Webinar

     February 23, 2019

     February 23, 2019

     07:00 AM PST

     09:00 AM PST

    Learn reading strategies that can help even non-voracious reader to master GMAT RC. Saturday, February 23rd at 7 AM PT

If the product of X and Y is a positive number, is the sum of X and Y

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

Hide Tags

 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 53063
If the product of X and Y is a positive number, is the sum of X and Y  [#permalink]

Show Tags

New post 31 May 2016, 04:46
1
3
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

63% (01:38) correct 37% (01:52) wrong based on 153 sessions

HideShow timer Statistics

Intern
Intern
User avatar
S
Joined: 21 Nov 2014
Posts: 31
Location: Viet Nam
GMAT 1: 760 Q50 V44
Re: If the product of X and Y is a positive number, is the sum of X and Y  [#permalink]

Show Tags

New post 31 May 2016, 18:33
If the product of x & y is a positive number --> we have 2 cases: both x & y are positive or both x & y are negative.

(1) x > y^5
With this information we can't tell the signs of x & y. If x = -1, y = -5 then the sum of x & y is negative. If x = 10 & y = 1 then the sum if positive.
-> Insufficient.
(2) x > y^6
With this information we can tell that x > 0 and hence y > 0 => sum of x & y > 0.
-> Sufficient.

Answer B.
_________________

GMAT Group for Vietnamese:

https://www.facebook.com/groups/644070009087525/

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6978
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: If the product of X and Y is a positive number, is the sum of X and Y  [#permalink]

Show Tags

New post 01 Jun 2016, 05:57
If we modify the original condition and the question, there are 2 variables (x and y), and 1 equation (xy>0). Hence, in order to match the number of variables to the number of equations, we need 1 more equation. Since the condition 1) and the condition 2) each has 1 equation, there is high chance that D is the correct answer.
From the condition 1), we can see that x=5, y=1 no, x-5, y=-2 yes. Hence, the condition is not sufficient.
From the condition 2), from x>y^6>=0, we can see x>0 and y>0. Since x+y>0, the answer is no and the condition is sufficient. Hence, the correct answer is B.
Attachments

variable approach's answer probability.jpg
variable approach's answer probability.jpg [ 219.74 KiB | Viewed 3501 times ]


_________________

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 $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Board of Directors
User avatar
P
Joined: 17 Jul 2014
Posts: 2587
Location: United States (IL)
Concentration: Finance, Economics
GMAT 1: 650 Q49 V30
GPA: 3.92
WE: General Management (Transportation)
GMAT ToolKit User Premium Member Reviews Badge
Re: If the product of X and Y is a positive number, is the sum of X and Y  [#permalink]

Show Tags

New post 03 Nov 2016, 05:59
Bunuel wrote:
If the product of X and Y is a positive number, is the sum of X and Y a negative number?

(1) X > Y^5
(2) X > Y^6


Looks like it's inequalities days for me today....
x and y can be either positive or negative - they need to have the same sign.

1. y can be -2, x can be -1. x+y is negative
y can be 1, x can be 2. x+y is positive.
1 alone is not sufficient. A and D are out.

2. x>y^6.
y^6 is always positive. it means that x is positive. since we know for sure that x and y must have the same sign, we can definitely give an answer to the question: the sum of X and Y is not a negative number!

B is the answer.
GMATH Teacher
User avatar
G
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 767
Re: If the product of X and Y is a positive number, is the sum of X and Y  [#permalink]

Show Tags

New post 09 Oct 2018, 10:40
Bunuel wrote:
If the product of X and Y is a positive number, is the sum of X and Y a negative number?

(1) X > Y^5
(2) X > Y^6

\(xy > 0\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\left( * \right)\,\,\,\,\left\{ \begin{gathered}
\,\,x > 0\,\,{\text{and}}\,\,y > 0\,\,\,\,\left( {{\text{scenario}}\,\,{\text{I}}} \right) \hfill \\
\,\,\,\,OR\,\,\, \hfill \\
\,\,x < 0\,\,{\text{and}}\,\,y < 0\,\,\,\,\left( {{\text{scenario}}\,\,{\text{II}}} \right) \hfill \\
\end{gathered} \right.\)

\(x + y\,\,\mathop < \limits^? \,\,\,0\,\,\,\,\,\,\mathop \Leftrightarrow \limits^{\left( * \right)} \,\,\,\boxed{\,\,\,?\,\,\,:\,\,\,{\text{scenario}}\,{\text{II}}\,\,}\)


\(\left( 1 \right)\,\,\,x > {y^5}\,\,\,\,\,\left\{ \begin{gathered}
\,{\text{Take}}\,\,\left( {x,y} \right) = \left( {2,1} \right)\,\,\,\,\, \Rightarrow \,\,\,\,\left\langle {{\text{NO}}} \right\rangle \,\, \hfill \\
\,{\text{Take}}\,\,\left( {x,y} \right) = \left( { - 1, - 2} \right)\,\,\,\, \Rightarrow \,\,\,\left\langle {{\text{YES}}} \right\rangle \,\, \hfill \\
\end{gathered} \right.\)

\(\left( 2 \right)\,\,x > {y^6}\,\, \geqslant 0\,\,\,\, \Rightarrow \,\,\,\,x > 0\,\,\,\,\,\mathop \Rightarrow \limits^{\left( * \right)} \,\,\,\,\left\langle {{\text{NO}}} \right\rangle \,\,\,\,\,\)


This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.
_________________

Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net

GMAT Club Bot
Re: If the product of X and Y is a positive number, is the sum of X and Y   [#permalink] 09 Oct 2018, 10:40
Display posts from previous: Sort by

If the product of X and Y is a positive number, is the sum of X and Y

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


Copyright

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

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

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®.