GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 20 Aug 2019, 07:44

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# If L1, L2 and L3 are lines in a plane, is L1 perpendicular

Author Message
TAGS:

### Hide Tags

Manager
Joined: 19 Oct 2010
Posts: 160
Location: India
GMAT 1: 560 Q36 V31
GPA: 3
If L1, L2 and L3 are lines in a plane, is L1 perpendicular  [#permalink]

### Show Tags

09 Apr 2011, 01:48
3
00:00

Difficulty:

5% (low)

Question Stats:

87% (00:49) correct 13% (01:00) wrong based on 155 sessions

### HideShow timer Statistics

If L1, L2 and L3 are lines in a plane, is L1 perpendicular to L3?

1. L1 is perpendicular to L2
2. L2 is perpendicular to L3

This may seem like an easy one! But I haven't been able to crack it!!

_________________
petrifiedbutstanding
Retired Moderator
Joined: 20 Dec 2010
Posts: 1716

### Show Tags

09 Apr 2011, 02:17
petrifiedbutstanding wrote:
If L1, L2 and L3 are lines in a plane, is L1 perpendicular to L3?

1. L1 is perpendicular to L2
2. L2 is perpendicular to L3

This may seem like an easy one! But I haven't been able to crack it!!

Combining both, we can conclude that either $$L1 || L3$$ OR "L1 coincides with L3"

$$L1 \hspace{3} \perp \hspace{3} L2$$

$$L2 \hspace{3} \perp \hspace{3} L3$$

$$L1 \hspace{3} || \hspace{3} L3$$ OR "L1 coincides with L3" but "L1 is not perpendicular to L3"

Ans: "C"

1. L1 is perpendicular to L2

Attachment:

l1_perp_l2.PNG [ 6.21 KiB | Viewed 9883 times ]

2. L2 is perpendicular to L3

Attachment:

l2_perp_l3.PNG [ 6.94 KiB | Viewed 9880 times ]

Combining both:

Attachment:

l1_perp_l2_perp_l3.PNG [ 4.28 KiB | Viewed 9866 times ]

_________________
Manager
Joined: 19 Oct 2010
Posts: 160
Location: India
GMAT 1: 560 Q36 V31
GPA: 3

### Show Tags

09 Apr 2011, 03:42
Hi Fluke,

Thanks. But doesn't the question clearly ask whether L1 is perp to L3, which is unanswerable with the given data?
_________________
petrifiedbutstanding
Retired Moderator
Joined: 20 Dec 2010
Posts: 1716

### Show Tags

09 Apr 2011, 03:49
petrifiedbutstanding wrote:
Hi Fluke,

Thanks. But doesn't the question clearly ask whether L1 is perp to L3, which is unanswerable with the given data?

I don't think so. It is a Yes/No question.

The definitive answer to the question is: "No, L1 is NOT perpendicular to L3". Why do you think it's unanswerable, please explain.
_________________
Manager
Joined: 19 Oct 2010
Posts: 160
Location: India
GMAT 1: 560 Q36 V31
GPA: 3

### Show Tags

09 Apr 2011, 04:59
No, you're right. I wrongly analysed it with the second statement.
_________________
petrifiedbutstanding
Intern
Joined: 21 Mar 2012
Posts: 1

### Show Tags

14 Apr 2012, 12:21
petrifiedbutstanding wrote:
No, you're right. I wrongly analysed it with the second statement.

If lines are perpendicular then
m1.m2=-1

Acc to 1) L1 is perpendi to L2 => m1.m2=-1 => m2=-1/m1, also cnt deduce whether L1 is perpendi to L3

Acc to 2) L2 is perpendi to L3 =>. m2.m3=-1 => cnt deduce whether L1 is perpendi to L3

Combine 1) and 2)

-1/m1 * m3=-1 =>m3/m1=1

Definitely L1 not perpendi to L3

So C)
Manager
Status: I will not stop until i realise my goal which is my dream too
Joined: 25 Feb 2010
Posts: 181
Schools: Johnson '15
Re: If L1, L2 and L3 are lines in a plane, is L1 perpendicular  [#permalink]

### Show Tags

14 Apr 2012, 22:03
petrifiedbutstanding wrote:
If L1, L2 and L3 are lines in a plane, is L1 perpendicular to L3?

1. L1 is perpendicular to L2
2. L2 is perpendicular to L3

This may seem like an easy one! But I haven't been able to crack it!!

Explanation :

Just pictorial representation helps resolve the above equation

1: L1 P L2 ...
no mention of L3...hence NOT SUFFICIENT
hence A and D options are not the answers

2: L2 P L3
no mention of L1, hence NOT SUFFICIENT
Hence Option B Is not answer

so left with C & E

together L1 P L2 P L3
by this , we can see that L1 is parallel to L3...
hence L1 is not perpendicular to L3...hence C is the answer
_________________
Regards,
Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat

Satyameva Jayate - Truth alone triumphs
IIMA, IIMC School Moderator
Joined: 04 Sep 2016
Posts: 1365
Location: India
WE: Engineering (Other)
Re: If L1, L2 and L3 are lines in a plane, is L1 perpendicular  [#permalink]

### Show Tags

23 Dec 2018, 08:44

Project DS Butler: Day 48: Data Sufficiency (DS95)

Bumping for DS Butler project.
_________________
It's the journey that brings us happiness not the destination.

Feeling stressed, you are not alone!!
Re: If L1, L2 and L3 are lines in a plane, is L1 perpendicular   [#permalink] 23 Dec 2018, 08:44
Display posts from previous: Sort by