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## GMAT Prep Ques (Equation of line)

This topic has 1 expert reply and 4 member replies
dferm Master | Next Rank: 500 Posts
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#### GMAT Prep Ques (Equation of line)

Fri Oct 03, 2008 7:31 am
In the xy-plane, the line with equation ax+by+c=o, where abc doesn't equal 0, has slope 2/3. What is the value of b?

(1) a = 4
(2) c = -6

Thanks.

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GMATGuruNY GMAT Instructor
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Mon Sep 18, 2017 3:10 am
dferm wrote:
In the xy-plane, the line with equation ax+by+c=o, where abc doesn't equal 0, has slope 2/3. What is the value of b?

(1) a = 4
(2) c = -6
Rephrase ax + by + c = 0 in the form y=mx + b:
ax + by + c = 0
by = -ax - c
y = (-a/b)x - c/b.

The expression in blue represents the slope of the line.
Since the line has a slope of 2/3, we get:
-a/b = 2/3.

The determine the value of b, we need to know the value of a.
Question stem, rephrased:
What is the value of a?

Statement 1: a=4.
SUFFICIENT.

Statement 2: c=-6.
INSUFFICIENT.

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YTarhouni Newbie | Next Rank: 10 Posts
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Sun Sep 17, 2017 9:08 pm
This is 750+ question.

it is definitely B.

any line will cross the X-ax if the slop is not zero.

A doesn't tell us anything about the slop
B tells us ab>0 hence neither a nor b equals zero. since -a/b is the slop of this line and since a is not zero, then the slop is not zero.

Morgoth Master | Next Rank: 500 Posts
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Fri Oct 03, 2008 9:15 am
dferm wrote:
In the xy-plane, the line with equation ax+by+c=o, where abc doesn't equal 0, has slope 2/3. What is the value of b?

(1) a = 4
(2) c = -6

Thanks.
For equation ax+by+c=o
slope = -a/b

statement (1)
a=4
-a/b = 2/3
-4/b=2/3
b=-6
Sufficient.

Statement (2) It does not give us anything to work with.

Thus, A.

OA?

dferm Master | Next Rank: 500 Posts
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Fri Oct 03, 2008 10:43 am
How are you getting -a/b? I believe the answer to be E...

Morgoth Master | Next Rank: 500 Posts
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Sat Oct 04, 2008 10:23 am
dferm wrote:
How are you getting -a/b? I believe the answer to be E...
Answer has to be A, kindly check the OA.

-a/b is a formula for slope

x intercept = -c/a

y- intercept = -c/b

Kindly refer the below link for further clarifications.

http://en.wikipedia.org/wiki/Slope

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