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

 It is currently 18 Dec 2018, 02:58

### 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

## Events & Promotions

###### Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• ### Happy Christmas 20% Sale! Math Revolution All-In-One Products!

December 20, 2018

December 20, 2018

10:00 PM PST

11:00 PM PST

This is the most inexpensive and attractive price in the market. Get the course now!
• ### Key Strategies to Master GMAT SC

December 22, 2018

December 22, 2018

07:00 AM PST

09:00 AM PST

Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.

# M18-13

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 51281

### Show Tags

16 Sep 2014, 00:03
00:00

Difficulty:

55% (hard)

Question Stats:

59% (01:20) correct 41% (01:40) wrong based on 41 sessions

### HideShow timer Statistics

If $$abc \ne 0$$ is the x-intercept of line $$ax+by+c=0$$ negative?

(1) $$ba \lt 0$$.

(2) $$ac \gt 0$$.

_________________
Math Expert
Joined: 02 Sep 2009
Posts: 51281

### Show Tags

16 Sep 2014, 00:03
Official Solution:

The x-intercept of a line is the value of $$x$$ when $$y=0$$. So, the x-intercept of line $$ax+by+c=0$$ is $$x=-\frac{c}{a}$$. Question basically asks: is $$-\frac{c}{a} \lt 0$$? Or: is $$\frac{c}{a} \gt 0$$? Or: do $$c$$ and $$a$$ have the same sign?

(1) $$ba \lt 0$$. Not sufficient as we cannot answer whether $$c$$ and $$a$$ have the same sign.

(2) $$ac \gt 0$$. From this statement it follows that $$c$$ and $$a$$ have the same sign. Sufficient.

_________________
Manager
Joined: 13 Dec 2013
Posts: 155
Location: United States (NY)
GMAT 1: 710 Q46 V41
GMAT 2: 720 Q48 V40
GPA: 4
WE: Consulting (Consulting)

### Show Tags

18 Mar 2017, 16:18
How do we know that x=-c/a?
Math Expert
Joined: 02 Sep 2009
Posts: 51281

### Show Tags

19 Mar 2017, 03:25
Cez005 wrote:
How do we know that x=-c/a?

The x-intercept of a line is the value of $$x$$ when $$y=0$$. Substitute y = 0 into $$ax+by+c=0$$ to get $$ax + c=0$$ --> $$x=-\frac{c}{a}$$.

Check for more here: https://gmatclub.com/forum/math-coordin ... 87652.html
_________________
Intern
Joined: 02 Jun 2016
Posts: 35
Location: India
GMAT 1: 660 Q44 V36
GMAT 2: 680 Q46 V38
GPA: 3.77
WE: General Management (Computer Software)

### Show Tags

15 Dec 2017, 01:18
But what if the original equation is modified to:
y= $$\frac{-a}{b}$$x - c ?

Then when we substitute y=0, x = -$$\frac{b}{a}$$c. For this, we need to know the signs of a,b and c! Which means, how can statement 2 alone be sufficient?
Math Expert
Joined: 02 Sep 2009
Posts: 51281

### Show Tags

15 Dec 2017, 01:22
helloksin wrote:
But what if the original equation is modified to:
y= $$\frac{-a}{b}$$x - c ?

Then when we substitute y=0, x = -$$\frac{b}{a}$$c. For this, we need to know the signs of a,b and c! Which means, how can statement 2 alone be sufficient?

If y = 0, the value of b does not play any role.
_________________
Manager
Joined: 17 Jul 2017
Posts: 116
Location: India
GMAT 1: 690 Q50 V33
GMAT 2: 750 Q50 V40
WE: Engineering (Manufacturing)

### Show Tags

15 Dec 2017, 02:01
helloksin wrote:
But what if the original equation is modified to:
y= $$\frac{-a}{b}$$x - c ?

Then when we substitute y=0, x = -$$\frac{b}{a}$$c. For this, we need to know the signs of a,b and c! Which means, how can statement 2 alone be sufficient?

The equation would become
y= $$\frac{-a}{b}x - \frac{c}{b}$$

So even in that case, for x intercept, y=0,
the equation boils down to x= $$\frac{-c}{a}$$

You missed the "b" in constant term.
Manager
Joined: 26 Feb 2018
Posts: 53
Location: India
GMAT 1: 560 Q41 V27
WE: Web Development (Computer Software)

### Show Tags

22 Jun 2018, 10:54
I think this is a high-quality question and I agree with explanation.
Re M18-13 &nbs [#permalink] 22 Jun 2018, 10:54
Display posts from previous: Sort by

# M18-13

Moderators: chetan2u, Bunuel

 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®.