1,q) is a point on line L. Is the slope of L greater than 0?

Question

(1,q) is a point on line L. Is the slope of L greater than 0?

(I) (q,1) is on L
(II) (13,q) is on L

MA · Answer

D.

from (I), slope = (1-q)/(q-1)=-(q-1)/(q-1)=-1, suff
from (II), slope = (q-q)/13-1=0 suff

rxs0005 · Answer

from I ) its always -ve 

from II) its 0 

so both suff D

HongHu · Answer

I got D too, but just realized why I was wrong. Anybody else has a clue?

HongHu · Answer

Good baner! :b:

OA is (B).

MA · Answer

baner and HongHu,


ok in (i) q = 1 

slope = (1-q)/(q-1)=(1-1)/(1-1)=0/0 = 0 or infinite or undefined or ??????

if it is 0, then ststement (i) is sufficiemnt.

guys pls explain........

HongHu · Answer

If q=1, (1,q) and (q,1) is one point. You need two points to determine a line. If you only have one point, there's no way you know if the slope is negative. Thus insufficient.

banerjeea_98 · Answer

HongHu explained it well enuf.....1 point can't give u a line....so insuff...also 0/0 is actually undefined.

MA · Answer

thanks guys. pretty clear......

ian7777 · Answer

If I can add a very important gmat point to this:

I was having a problem with this problem. I guess D should have worked, because both point to a specific situation in which we can know about the slope. But what I didn't like was that the two statements seemed to point to two different lines.

In the second statment, we see that the line L must be a straight, horizontal line, with slope 0. That's fine, and difinitive enought. But in statement number one, we see that the line must have two different points at two different locations. We get a positive slope, so we can answer the question, but it's not 0, which it was in number 2.

I was about to comment that this couldn't be a real GMAT question, because the two statments always have to speak about the same answer. And here is my point: you will never get D in a way that the two statements both work but both point to a different answer.

If this happened on the test, I would have been forced to think about it again. And then I realized that q could be 1, which would derail statement 1 as enough, but it would then allow the line L to have a slope of zero.

So remember that. If they don't match up, then you're missing something.

HongHu · Answer

C means you could get a solution by working both conditions together.

D means each of the two conditions can give you an answer indepently. They don't have to give you the same answer. In this question, if (I) says 1<>1, then the answer would indeed be D.

ian7777 · Answer

HongHu, this is simply not the case. The writer of a data sufficiency question has a specific answer in mind, and writes the question to that answer. The statements go some or all of the way towards getting that answer, but they never speak about different situations entirely.

I will bet my business on it. This is a terribly important nuance that people taking the GMAT would be well served to understand. Once you do, you can learn how to use the answer choices to get information about hte problem, even if you're not choosing C, as I did in the example above.

HongHu · Answer

Hmmm, I could almost swear that I've seen questions where (i) and (ii) leads to different answers but both are sufficient indepently (thus (D)). I'll let you know if I see one like this. You may very well be right. But I'm still a bit suspicious to this. It's almost adding a new assumption of yourself to a question. I wouldn't do it if I have other ways to solve a question.

ian7777 · Answer

The question is whether or not you have seen them on real test examples or on boards or from other sources. Many people developing questions do not recognize this nuance. But go through the DS section of the entire OG, for example, and you will not find one example of this. I can show you a thousand other data sufficiencies. Not a single one will ever have the two statements contradicting each other.

If you do find one, I'll be happy to explore it.

praveen_rao7 · Answer

I agree with ian7777,

Most ETS questions with choice D refers to same answer

MA · Answer

Thanks Ian for more clearification.....................

swath20 · Answer

I agree with Ian. But I have seen questions where the statements contradict each other... But never in the questions from the OG. These questions are always from other sources....

1,q) is a point on line L. Is the slope of L greater than 0?

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