Target Test Prep is 20% off right now!
Use code FLASH20
Available with Beat the GMAT members only code
MORE DETAILS
Coordinate Plane - GMAT Prep
This topic has expert replies
GMAT/MBA Expert
-
ceilidh.erickson
- GMAT Instructor
- Posts: 2095
- Joined: Tue Dec 04, 2012 3:22 pm
- Thanked: 1443 times
- Followed by:247 members
The question is asking if this particular line crosses the x-axis. Try thinking about the opposite: the only lines that will never cross the x-axis are horizontal lines. Horizontal lines have a slope of 0.Does the line with the equation ax + by = c, where a, b, cand c are real constants, cross the x-axis?
(1) b ≠0
(2) ab > 0
Rephrased question: does the line have a non-zero slope?
First, rearrange the the equation into y = mx + b form:
y = (-ax)/b + c/b
Thus, the slope = -a/b
The only way for this slope to be 0 is is a = 0. So rephrase again:
Further rephrased question: Does the variable a represent a non-zero number?
(1) b ≠0
This tells us nothing about a. Insufficient.
(2) ab > 0
If the product of a and b is greater than 0, then a ≠0. Sufficient!
The answer is B.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
-
DavidG@VeritasPrep
- Legendary Member
- Posts: 2663
- Joined: Wed Jan 14, 2015 8:25 am
- Location: Boston, MA
- Thanked: 1153 times
- Followed by:128 members
- GMAT Score:770
After you review Ceilidh's elegant solution, go back and ask yourself: how does the answer change if the question had asked if the line crosses the y-axis?Does the line with the equation ax + by = c, where a, b, and c are real constants, cross the x-axis?
(1) b ≠0
(2) ab > 0
-
Neilsheth2
- Senior | Next Rank: 100 Posts
- Posts: 65
- Joined: Sun Jun 03, 2012 8:58 am
- Thanked: 1 times
Hey correct me if I am wrong so now the question rephrased would be whether the slope is undefined? That can be only done if the denominator is 0.DavidG@VeritasPrep wrote:After you review Ceilidh's elegant solution, go back and ask yourself: how does the answer change if the question had asked if the line crosses the y-axis?Does the line with the equation ax + by = c, where a, b, and c are real constants, cross the x-axis?
(1) b ≠0
(2) ab > 0
A- states it cant be 0 so SUFF
b- states that the slope is some number so again SUFF
Therefore D.
-
DavidG@VeritasPrep
- Legendary Member
- Posts: 2663
- Joined: Wed Jan 14, 2015 8:25 am
- Location: Boston, MA
- Thanked: 1153 times
- Followed by:128 members
- GMAT Score:770
ExactlyNeilsheth2 wrote:Hey correct me if I am wrong so now the question rephrased would be whether the slope is undefined? That can be only done if the denominator is 0.DavidG@VeritasPrep wrote:After you review Ceilidh's elegant solution, go back and ask yourself: how does the answer change if the question had asked if the line crosses the y-axis?Does the line with the equation ax + by = c, where a, b, and c are real constants, cross the x-axis?
(1) b ≠0
(2) ab > 0
A- states it cant be 0 so SUFF
b- states that the slope is some number so again SUFF
Therefore D.
