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

 It is currently 19 Oct 2019, 10:53

### 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

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

# Is xy>0?

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 8017
GMAT 1: 760 Q51 V42
GPA: 3.82

### Show Tags

28 Aug 2018, 02:06
00:00

Difficulty:

25% (medium)

Question Stats:

77% (01:21) correct 23% (01:01) wrong based on 55 sessions

### HideShow timer Statistics

[Math Revolution GMAT math practice question]

Is $$xy>0$$?

$$1) x+y>0$$
$$2) |x|+|y|<1$$

_________________
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" NUS School Moderator Joined: 18 Jul 2018 Posts: 1021 Location: India Concentration: Finance, Marketing WE: Engineering (Energy and Utilities) Re: Is xy>0? [#permalink] ### Show Tags 28 Aug 2018, 02:44 1 From statement 1: No info about X and Y. If X is +0.9 and Y is -0.4 Then X+Y = 0.5>0 But XY<0 and, If X = 1 and Y is 2 then X+Y = 3>0 and XY>0. Both cases possible. Insufficient. From statement 2: |x|+|y|<1 |X|<1 and |Y|<1 Same cases as statement 1. Insufficient. Combining also doesn't give a unique answer. E is the answer. _________________ Press +1 Kudos If my post helps! GMAT Club Legend Joined: 12 Sep 2015 Posts: 4009 Location: Canada Re: Is xy>0? [#permalink] ### Show Tags 28 Aug 2018, 08:11 Top Contributor MathRevolution wrote: [Math Revolution GMAT math practice question] Is $$xy>0$$? $$1) x+y>0$$ $$2) |x|+|y|<1$$ Target question: Is xy>0? Statement 1: x + y > 0 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 = 1. In this case, xy = (1)(1) = 1. So, the answer to the target question is YES, xy IS greater than 0 Case b: x = 2 and y = -1. In this case, xy = (2)(-1) = -2. So, the answer to the target question is NO, xy is NOT greater than 0 Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT Aside: For more on this idea of testing values when a statement doesn't feel sufficient, read my article: http://www.gmatprepnow.com/articles/dat ... lug-values Statement 2: |x| + |y| < 1 Let's test values again. Case a: x = 0.2 and y = 0.2. In this case, xy = (0.2)(0.2) = 0.04. So, the answer to the target question is YES, xy IS greater than 0 Case b: x = -0.8 and y = 0.1. In this case, xy = (-0.8)(0.1) = -0.08. So, the answer to the target question is NO, xy is NOT greater than 0 Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT Statements 1 and 2 combined There are still several values of x and y that satisfy BOTH statements. Here are two: Case a: x = 0.2 and y = 0.2. In this case, xy = (0.2)(0.2) = 0.04. So, the answer to the target question is YES, xy IS greater than 0 Case b: x = 0.8 and y = -0.1. In this case, xy = (0.8)(-0.1) = -0.08. So, the answer to the target question is NO, xy is NOT greater than 0 Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT Answer: E Cheers, Brent _________________ Test confidently with gmatprepnow.com Senior Manager Joined: 07 Oct 2017 Posts: 253 Re: Is xy>0? [#permalink] ### Show Tags 28 Aug 2018, 08:49 MathRevolution wrote: [Math Revolution GMAT math practice question] Is $$xy>0$$? $$1) x+y>0$$ $$2) |x|+|y|<1$$ Answer is E Attachment: 1535471463904.jpg [ 51.71 KiB | Viewed 629 times ] Thank you = Kudos _________________ Thank you =Kudos The best thing in life lies on the other side of the pain. Manager Joined: 06 Nov 2016 Posts: 58 Location: Viet Nam Concentration: Strategy, International Business GPA: 3.54 Re: Is xy>0? [#permalink] ### Show Tags 28 Aug 2018, 09:56 MathRevolution wrote: [Math Revolution GMAT math practice question] Is $$xy>0$$? $$1) x+y>0$$ $$2) |x|+|y|<1$$ I think the quickest way to solve this question is number plugging. When the question is whether xy > 0 or xy < 0, I usually select number 0 to test the statement. (1) x+y>0. If x=0, y=0.5 -> No. If x=0.1, y=0.5 -> Yes. --> Not sufficient. (2) |x|+|y|<1. If x=0, y=0.5 -> No. If x=0.1, y=0.5 -> Yes. --> Not sufficient. (1) + (2) Two possible answers still exist. --> Not sufficient. Answer E. _________________ Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 8017 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Is xy>0? [#permalink] ### Show Tags 30 Aug 2018, 00:49 => Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. Since we have 2 variables ($$x$$ and $$y$$) and $$0$$ equations, C is most likely to be the answer. So, we should consider conditions 1) & 2) together first. After comparing the number of variables and the number of equations, we can save time by considering conditions 1) & 2) together first. Conditions 1) & 2) If $$x = \frac{1}{2}$$ and $$y = \frac{1}{4}$$, then $$xy > 0$$ and the answer is ‘yes’. If $$x = \frac{1}{2}$$ and $$y = -(\frac{1}{4})$$, then $$xy < 0$$ and the answer is ‘no’. Since the answer is not unique, both conditions are not sufficient, when taken together. Therefore, E is the answer. Answer: 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"
Re: Is xy>0?   [#permalink] 30 Aug 2018, 00:49
Display posts from previous: Sort by