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Parallel lines

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Parallel lines

by sparkles3144 » Tue May 21, 2013 10:34 am
If each of the two lines L1 and L2 is parallel to line L3, which of the following must be true?

A. Lines L1,L2, and L3 lie in same plane.
B. Lines L1,L2,L3 lie in different planes.
C. Line L1 is parallel to L2
D. Line L1 is same line as L2
E. Line L1 is the same line as L3

I was confued between A and C

My question:
Can parallel lines be in same plane? If so, what are the conditions?

Please let me know.

Thanks!
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by Jim@StratusPrep » Tue May 21, 2013 10:56 am
Where did you find this question? I have never seen anything about planes in all of my GMAT work...
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by sparkles3144 » Tue May 21, 2013 11:04 am
Thank you for replying.

I bought retired GMAT questions from MBA.com online store.
https://www.mba.com/store/store-catalog/ ... ction.aspx
I found it in Test Code 25.

Did GMAT change over the years?
Can I just skip planes and parallel lines?
Please let me know!
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by Jim@StratusPrep » Wed May 22, 2013 5:01 am
Huh. Interesting. A) must be correct because there [in C] is the possibility that the L1 and L2 are the same line and thus would not be parallel - and parallel lines must be on the same plane.
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by Brent@GMATPrepNow » Wed May 22, 2013 6:26 am
sparkles3144 wrote:If each of the two lines L1 and L2 is parallel to line L3, which of the following must be true?

A. Lines L1,L2, and L3 lie in same plane.
B. Lines L1,L2,L3 lie in different planes.
C. Line L1 is parallel to L2
D. Line L1 is same line as L2
E. Line L1 is the same line as L3
I think the answer is C

In the diagram below, we can see that L1 and L2 are parallel to line L3, but all 3 lines are not in the same plane. So we can eliminate A.
Image

However, if L1 and L2 are parallel to line L3, then L1 and L2 must be parallel C.

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by Atekihcan » Wed May 22, 2013 7:02 am
I agree with Brent.
If two lines are parallel to each other, they must lie on the same plane. However, if three lines are parallel to each other, then they may or may not lie on the same plane but each pair of them will always lie on the same plane.

And 'two lines are same' is basically a special case of 'two lines are parallel to each other'.
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by Navinag » Thu May 23, 2013 6:53 am
Jim@StratusPrep wrote:Huh. Interesting. A) must be correct because there [in C] is the possibility that the L1 and L2 are the same line and thus would not be parallel - and parallel lines must be on the same plane.
I'm not sure if I'll take 'the L1 and L2 being part of same line' as not being parallel. They'll satisfy the requirements of being in the same plane and orientation for being parallel. Am I missing something ?
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