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Line l lies in the xy-plane and does not pass through the origin. What

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Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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Line \(\ell\) lies in the xy-plane and does not pass through the origin. What is the slope of line \(\ell\) ?

(1) The x-intercept of line \(\ell\) is twice the y-intercept of line \(\ell\)
(2) The x-and y-intercepts of line \(\ell\) are both positive
[Reveal] Spoiler: OA

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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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AbdurRakib wrote:
Line \(\ell\) lies in the xy-plane and does not pass through the origin. What is the slope of line \(\ell\) ?

(1) The x-intercept of line \(\ell\) is twice the y-intercept of line \(\ell\)
(2) The x-and y-intercepts of line \(\ell\) are both positive


Target question: What is the slope of line l?

Statement 1: The x-intercept of line \(\ell\) is twice the y-intercept of line l
Let k = the y-intercept of line l
This means 2k = the x-intercept of line l
If the y-intercept is k, then line l passes through the y-axis at the point (0, k)
If the x-intercept is 2k, then line l passes through the x-axis at the point (2k, 0)
Since (0, k) and (2k, 0) are both points on line l, we can apply the slope formula to these points to find the slope of line l.
We get: slope = (k - 0)/(0 - 2k) = k/(-2k) = -1/2
So, the slope of line l = -1/2
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: The x-and y-intercepts of line l are both positive
If we're able to imagine different lines (with DIFFERENT SLOPES) that satisfy this condition, we'll quickly see that statement 2 is not sufficient. However, if we don't automatically see this, we can take the following approach...
There are many different cases that satisfy statement 2 yet yield different answers to the target question. Here are two:
Case a: the x-intercept is 1 and the y-intercept is 1, which means line l passes through (1, 0) and (0, 1). Applying the slope formula, we get: slope = (0 - 1)/(1 - 0) = -1
Case b: the x-intercept is 2 and the y-intercept is 1, which means line l passes through (2, 0) and (0, 1). Applying the slope formula, we get: slope = (0 - 1)/(2 - 0) = -1/2
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Answer:
[Reveal] Spoiler:
A


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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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AbdurRakib wrote:
Line \(\ell\) lies in the xy-plane and does not pass through the origin. What is the slope of line \(\ell\) ?

(1) The x-intercept of line \(\ell\) is twice the y-intercept of line \(\ell\)
(2) The x-and y-intercepts of line \(\ell\) are both positive


When I see something like this, I just start drawing. For me, it's easier to look at the slopes and compare them, versus trying to understand the slopes based on numbers and equations.

For statement 1, draw a couple of lines that have an x-intercept twice the y-intercept. Don't forget negatives (for instance, x-intercept of -2 and y-intercept of -1). You should notice that all of the slopes of these lines are equal.

Image

Note that this is an example of a DS problem with a 'nice but not necessary' statement. Be very careful to analyze the statements each on their own before putting them together. It's nice to know that the slopes are both positive (statement 2), because it gives you a clearer picture of what's going on. But critically, it's not necessary to know that. You can answer the question even without it.
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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 20 Jun 2017, 19:49
Dear ccooley and Brent,

I have a question. You both consider the slop is negative., while it could be positive too. For example, the line could intersect the 'y' in point (0,1) and 'x' in point (-2,0). This line satisfies the condition too. What did not you take it into consideration?

Thanks

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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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Mo2men wrote:
Dear ccooley and Brent,

I have a question. You both consider the slop is negative., while it could be positive too. For example, the line could intersect the 'y' in point (0,1) and 'x' in point (-2,0). This line satisfies the condition too. What did not you take it into consideration?

Thanks


In your example, the x-intercept is -2 and the y-intercept is 1

However, statement 1 says that the x-intercept twice the y-intercept.
-2 is not twice 1

Cheers,
Brent
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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 21 Jun 2017, 00:54
GMATPrepNow wrote:
Mo2men wrote:
Dear ccooley and Brent,

I have a question. You both consider the slop is negative., while it could be positive too. For example, the line could intersect the 'y' in point (0,1) and 'x' in point (-2,0). This line satisfies the condition too. What did not you take it into consideration?

Thanks


In your example, the x-intercept is -2 and the y-intercept is 1

However, statement 1 says that the x-intercept twice the y-intercept.
-2 is not twice 1

Cheers,
Brent


Thanks Brent. What I understand from Fact 1 is the that 'twice' means x-intercept 'double' the y-intercept regardless of any sign. It treated the intercept as distance from zero to the intercept regardless the sign. Where is the problem in my understanding?

Thanks in advance

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Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 21 Jun 2017, 03:35
AbdurRakib wrote:
Line \(\ell\) lies in the xy-plane and does not pass through the origin. What is the slope of line \(\ell\) ?

(1) The x-intercept of line \(\ell\) is twice the y-intercept of line \(\ell\)
(2) The x-and y-intercepts of line \(\ell\) are both positive


This question requires no pen to paper. From 1 we know that slope is .5 regardless of the signs of the x and y-intercepts (2). 2 is basically irrelevant and insufficient without knowing the values. Hence A, 1 alone is sufficient.

Last edited by rulingbear on 22 Jun 2017, 18:34, edited 1 time in total.

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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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Mo2men wrote:
Thanks Brent. What I understand from Fact 1 is the that 'twice' means x-intercept 'double' the y-intercept regardless of any sign. It treated the intercept as distance from zero to the intercept regardless the sign. Where is the problem in my understanding?

Thanks in advance


I think you might be confusing the x- and y-intercepts with the DISTANCE from the origin.
An x-intercept of -2 is 2 units away from the origin (0,0) and a y-intercept of 1 is 1 units away from the origin.


Cheers,
Brent
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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 22 Jun 2017, 14:39
GMATPrepNow wrote:
Mo2men wrote:
Thanks Brent. What I understand from Fact 1 is the that 'twice' means x-intercept 'double' the y-intercept regardless of any sign. It treated the intercept as distance from zero to the intercept regardless the sign. Where is the problem in my understanding?

Thanks in advance


I think you might be confusing the x- and y-intercepts with the DISTANCE from the origin.
An x-intercept of -2 is 2 units away from the origin (0,0) and a y-intercept of 1 is 1 units away from the origin.


Cheers,
Brent



Yes, it really was my understanding.

Thanks for your support

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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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y=ax+ b
x intercept mean y=0
x= -b/a
y intercept mean x=0
y =b
I have no
-b/a=2b

we can infer a, which is slope

dont draw anything.
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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 28 Oct 2017, 06:55
victory47 wrote:
y=ax+ b
x intercept mean y=0
x= -b/a
y intercept mean x=0
y =b
I have no
-b/a=2b

we can infer a, which is slope

dont draw anything.


Hi Victory,

This is a clear explanation, however for some reason I have troubles getting to the point where -b/a = 2b. Can you explain how you got there step by step?

Much appreciated!

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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 30 Oct 2017, 02:50
Line ℓ lies in the xy-plane and does not pass through the origin. What is the slope of line ℓ ?

(1) The x-intercept of line ℓ is twice the y-intercept of line ℓ

(2) The x-and y-intercepts of line ℓ are both positive.

Guys - Are we not talking about absolute values of the x & y intercept? How can we infer that even the signs have to be same for the intercepts.

X intercept = -4 & y intercept = 2 - this will make the statement 1 insufficient.

the statement as such does refer to the magnitude only and not the signs .

@experts - please help.

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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 30 Oct 2017, 07:15
Leo8 wrote:
Line ℓ lies in the xy-plane and does not pass through the origin. What is the slope of line ℓ ?

(1) The x-intercept of line ℓ is twice the y-intercept of line ℓ

(2) The x-and y-intercepts of line ℓ are both positive.

Guys - Are we not talking about absolute values of the x & y intercept? How can we infer that even the signs have to be same for the intercepts.

X intercept = -4 & y intercept = 2 - this will make the statement 1 insufficient.

the statement as such does refer to the magnitude only and not the signs .

@experts - please help.



hi...
when we talk of intercept and say y-intercept is 2, it means 2 and not -2..
the intercepts are never the absolute values but exact value..

we always say y- intercept or x- intercept is -2 and so on
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Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink]

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New post 17 Nov 2017, 11:47
AbdurRakib wrote:
Line \(\ell\) lies in the xy-plane and does not pass through the origin. What is the slope of line \(\ell\) ?

(1) The x-intercept of line \(\ell\) is twice the y-intercept of line \(\ell\)
(2) The x-and y-intercepts of line \(\ell\) are both positive


We need to determine the slope of line ℓ, given that it doesn’t pass through the origin.

Statement One Alone:

The x-intercept of line ℓ is twice the y-intercept of line ℓ.

We can let b = the y-intercept of line ℓ; thus, 2b = the x-intercept of line ℓ. Thus, the two points through which line ℓ passes are (2b, 0) and (0, b). With two points known, we can calculate the slope of line ℓ:

(b - 0)/(0 - 2b) = b/(-2b) = -½

Statement one alone is sufficient to answer the question.

Statement Two Alone:

The x- and y-intercepts of line ℓ are both positive.

Knowing that both the x- and y-intercepts of a line are positive does not allow us to determine the slope of the line. For example, the slope of the line with x-intercept = 1 and y-intercept = 2 will be different from the slope of the line with x-intercept = 1 and y-intercept = 3. Statement two alone is not sufficient to answer the question.

Answer: A
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Re: Line l lies in the xy-plane and does not pass through the origin. What   [#permalink] 17 Nov 2017, 11:47
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