In the x–y plane, what is the y–intercept of the line l? : GMAT Data Sufficiency (DS)
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# In the x–y plane, what is the y–intercept of the line l?

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In the x–y plane, what is the y–intercept of the line l? [#permalink]

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16 Feb 2012, 16:35
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In the x–y plane, what is the y–intercept of the line l?

(1) The slope of the line l is 3 times its y-intercept.
(2) The x–intercept of line l is –1/3

As the OA is not given, I have arrived at answer C i.e both statements together are sufficient to answer the question. Please see below what makes me say this. Please let me know whether I am right or wrong.

Equation of line y = mx+c ------------------------------(1). Question is asking to find C.

Considering Statement 1 ----> m = 3c. So putting this value of m in (1) above we get y = c(3x+1). Not sufficient.

Considering Statement 2 ---> x intercept is -1/3 i.e. y = -m/3+c. -------------------------------(2)
Can't solve for C. Therefore insufficient.

Combining the statement 1 & 2 and substituting the value of m = 3c from statement 1 into statement 2. y = -3c/3+c => c-c = 0 Therefore, y = 0. Therefore C is the right answer.
[Reveal] Spoiler: OA

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Last edited by Bunuel on 02 Jun 2012, 11:34, edited 2 times in total.
Edited the question and added the OA
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Re: Y intercept of line l [#permalink]

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16 Feb 2012, 20:14
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Expert's post
In the x–y plane, what is the y–intercept of the line l?

Equation of a line in point intercept form is $$y=mx+b$$, where: $$m$$ is the slope of the line; $$b$$ is the y-intercept of the line (the value of $$y$$ for $$x=0$$).

The question is $$b=?$$

(1) The slope of line l is 3 times its y-intercept --> $$m=3b$$. Not sufficient to calculate $$b$$.

(2) The x-intercept of line l is -1/3 --> x-intercept is the value of $$x$$ for $$y=0$$ --> $$0=-\frac{1}{3}m+b$$ --> $$m=3b$$. Same info as above. Not sufficient.

(1)+(2) Nothing new. Not sufficient.

For more on this issue please check Coordinate Geometry chapter of Math Book: math-coordinate-geometry-87652.html

Hope it helps.
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In the x–y plane, what is the y–intercept of the line l? [#permalink]

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02 Jun 2012, 08:47
revised.
I got it and have no question
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Last edited by LalaB on 02 Jun 2012, 09:43, edited 1 time in total.
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Re: In the xy-plane, what is the y-intercept of line? [#permalink]

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02 Jun 2012, 09:39
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Say the line is:
Y=mX+b
The question is: b=?
Statement 1: m=3b, b=m/3, we do not know the value of m
so b cannot be determined. Insufficient

Statement2: by plugging in point (0, -1/3), we get
0=-m/3+b or m=3b. same as statement 1. Insufficient

Together: since, both are the same statement and both are insufficient, the answer is E.
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Re: In the x–y plane, what is the y–intercept of the line l? [#permalink]

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20 Dec 2015, 13:15
since the answer is confirmed at E, can the answer in the first post be updated? When I clicked E for my answer, it showed that the correct answer is C.
Re: In the x–y plane, what is the y–intercept of the line l?   [#permalink] 20 Dec 2015, 13:15
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