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#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  # Line l lies in the xy-plane and does not pass through the origin. What

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

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Question Stats: 52% (01:34) correct 48% (01:26) wrong based on 1459 sessions

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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
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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

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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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6
1
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.
##### General Discussion
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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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1
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. 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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Schools: Erasmus '21 (M$) Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink] ### Show Tags Dear ccooley and Brent, I have a question. You both consider the slop is negative., while it could be positive too. For example, the line could intersect the 'y' in point (0,1) and 'x' in point (-2,0). This line satisfies the condition too. What did not you take it into consideration? Thanks GMAT Club Legend  V Joined: 12 Sep 2015 Posts: 4214 Location: Canada Re: Line l lies in the xy-plane and does not pass through the origin. What [#permalink] ### Show Tags 1 Top Contributor Mo2men wrote: Dear ccooley and Brent, I have a question. You both consider the slop is negative., while it could be positive too. For example, the line could intersect the 'y' in point (0,1) and 'x' in point (-2,0). This line satisfies the condition too. What did not you take it into consideration? Thanks In your example, the x-intercept is -2 and the y-intercept is 1 However, statement 1 says that the x-intercept twice the y-intercept. -2 is not twice 1 Cheers, Brent _________________ SVP  V Joined: 26 Mar 2013 Posts: 2345 Concentration: Operations, Strategy Schools: Erasmus '21 (M$)
Re: Line l lies in the xy-plane and does not pass through the origin. What  [#permalink]

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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?

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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

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.

Originally posted by rulingbear on 21 Jun 2017, 04:35.
Last edited by rulingbear on 22 Jun 2017, 19:34, 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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Top Contributor
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?

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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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?

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.

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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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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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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 .

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Joined: 02 Aug 2009
Posts: 8343
Re: Line l lies in the xy-plane and does not pass through the origin. What  [#permalink]

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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 .

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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4
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.

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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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@Bunuel,@Veritasprepkarishma, chetan2u, mikemcgarry. I am really struggling with these types Co. geometry problems. Could you please share your detailed approach to this problem. 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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3
Line L is in the form of Y= mx + b (Here, m is the slope)

St 1: Y-intercept = b so, x-intercept = 2b

In general, We know from the equation of any line
Y-intercept = b (when x=0)
x-intercept = -b/m (when y=0)

Now replace the value x=2b, we get 2b = -b/m or m = - 1/2 Sufficient

St 2: No specific value or no relation is given. Insufficient.

Ans 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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BalysLTU wrote:
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!

In the statement it asked to take twice.

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

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1
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

First, try to break down the question stem as much as possible.
Assume: y=kx+b, we need to find out the value of k or k= (y-b)/x

Statement 1:
To find out the value of x (X-intercept), let y=0, x= -b/k;
To find out the value of y (Y-intercept), let x=0, y=b;
Given that x=2y, -b/k=2b, divide b on both sides of the equation, we get -1/k=2, and we find out the value of k. We don't even need to calculate and find out the exact value of k, we just know that we get a confirmed value of K, hence Statement 1 is SUFFICIENT.

Statement 2:
Given that x and y are both positive, we need to find out k= (y-b)/x;
We are unable to find a definite value of k, hence Statement 2 is NOT SUFFICIENT. Line l lies in the xy-plane and does not pass through the origin. What   [#permalink] 08 Jun 2019, 06:13
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