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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 \(x=0\)); \(x\) is the independent variable of the function \(y\).

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 (link in my signature).

Re: What is the y-intercept of the line [#permalink]

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18 Sep 2010, 15:26

2

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To find: y-intercept of the line. When the line intercepts the y axis, x=0. Hence the original equation y=mx+c becomes y=c. Question asks for the value of c. Statement 1: Slope of the line is 3 times the y intercept. Hence m = 3c. Insufficient.

Statement 2: The x intercept is -1/3. x intercept means y is zero. Hence the original line equation becomes 0=m(-1/3) +c

m = 3c. Same as the first equation. Insufficient.

Combining both yields nothing. Hence the answer is E.
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Both equations unsolvable. insuff. E
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DS - If negative answer only, still sufficient. No need to find exact solution. PS - Always look at the answers first CR - Read the question stem first, hunt for conclusion SC - Meaning first, Grammar second RC - Mentally connect paragraphs as you proceed. Short = 2min, Long = 3-4 min

I approached this problem as: y = mx + c.....equation of line... (1)

to find C

1) m = 3c.... (2)

substitute (2) in (1)

y = 3cx + c y = c(3x +1)...... (3)

2) X intercept = -1/3

2 implies the line passes through (-1/3,0) doesnt give enough info for M

Combined substitute point (-1/3,0) in (3)

0 = c(3 * -1/3 +1) 0 = c (-1+1 ) c = 0 ?

what did i do wrong ?

From 0=c(-1+1) --> 0=c*0, which holds true for ANY value of c not only for c=0. Also, notice that if c=0, then m=0, thus our line is y=0 which contradicts the statements.

Re: In the xy-plane, what is the y-intercept of line l? [#permalink]

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30 Sep 2013, 12:35

testprep2010 wrote:

In the xy-plane, what is the y-intercept of line l?

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

1. y=mx+c

given >> m=3c

y=3cx+c

when y=0, x=-1/3 .. from point -1/3,0 we can draw 2 lines satisfying the condition given above, one with obtuse angle(-ve y intercept) and other with acute angle(+ve y intercept) .. hence, not sufficient

2. x=-1/3 we can draw infinite lines passing from this point .. very clear ..
_________________

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 \(x=0\)); \(x\) is the independent variable of the function \(y\).

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 (link in my signature).

Hope it helps.

Hi Bunuel,

In every DS question, if both statements provide the exact same insufficient information and that information is derived in different ways ( slope in (1) and x-intercept in (2) ) , can we assume that both together are insufficient?

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 \(x=0\)); \(x\) is the independent variable of the function \(y\).

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 (link in my signature).

Hope it helps.

Hi Bunuel,

In every DS question, if both statements provide the exact same insufficient information and that information is derived in different ways ( slope in (1) and x-intercept in (2) ) , can we assume that both together are insufficient?

Hi Toolong150,

Do not assume anything on DS question unless and until it is obvious.

To your above question, If you get same insufficient information from both statements then ans is E as is above the case. If you look at the above question,actually both statement tell you the same thing but in st1 it talks about slope and st 2 it talks about x intercept

St 1 y= mx+ c says m =3c now if you find x intercept (y=0) we get 0=3cx+c or x=-1/3

Same as st 2

Hope it helps
_________________

“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”

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 \(x=0\)); \(x\) is the independent variable of the function \(y\).

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 (link in my signature).

Hope it helps.

Hi Bunuel,

I realize that "b' is the y intercept in the equation y = mx + b.

-That being said, I was a little confused as to whether I should solve for B or solve for Y by equation x to 0. If I did the latter, i would get y = b.

-How do I know I I should plug in values for X and Y or solve for B? This part seems to give me the most trouble.

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 \(x=0\)); \(x\) is the independent variable of the function \(y\).

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 (link in my signature).

Hope it helps.

Hi Bunuel,

I realize that "b' is the y intercept in the equation y = mx + b.

-That being said, I was a little confused as to whether I should solve for B or solve for Y by equation x to 0. If I did the latter, i would get y = b.

-How do I know I I should plug in values for X and Y or solve for B? This part seems to give me the most trouble.

Thanks

y = b cannot be sufficient. When a DS question asks about the value of some variable, then the statement(s) is sufficient ONLY if you can get the single numerical value of this variable.

Re: In the xy-plane, what is the y-intercept of line l? [#permalink]

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01 Feb 2017, 17:12

If the slope and y-intercept of a line in xy plane are m and c respectively, then the line can be represented by the equation y = mx + c and the x=intercept of the line will be -c/m

Statement 1: m = 3c ---> Not sufficient

Statement 2: -c/m = -1/3 ---> m = 3c ---> Not sufficient

1 & 2 Together: We have no new information ---> Not sufficient

Re: In the xy-plane, what is the y-intercept of line l? [#permalink]

Show Tags

06 May 2017, 12:23

stunn3r wrote:

testprep2010 wrote:

In the xy-plane, what is the y-intercept of line l?

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

1. y=mx+c

given >> m=3c

y=3cx+c

when y=0, x=-1/3 .. from point -1/3,0 we can draw 2 lines satisfying the condition given above, one with obtuse angle(-ve y intercept) and other with acute angle(+ve y intercept) .. hence, not sufficient

2. x=-1/3 we can draw infinite lines passing from this point .. very clear ..

Can you elaborate on your reasoning for 2). Not any line would suffice, would it? The line would still have to have m=3c.