In the xy-plane, line a and line b have the same slope. : GMAT Data Sufficiency (DS)
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 23 Jan 2017, 22:39

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# In the xy-plane, line a and line b have the same slope.

Author Message
TAGS:

### Hide Tags

Manager
Joined: 14 Mar 2010
Posts: 82
Followers: 2

Kudos [?]: 135 [0], given: 44

In the xy-plane, line a and line b have the same slope. [#permalink]

### Show Tags

24 Apr 2012, 19:54
1
This post was
BOOKMARKED
00:00

Difficulty:

45% (medium)

Question Stats:

65% (02:16) correct 35% (00:47) wrong based on 110 sessions

### HideShow timer Statistics

In the xy-plane, line a and line b have the same slope. If the y-intercept of line a is -1, what is the y-intercept of line b ?

(1) The x-intercept of line a is -1. We have two points of line a: (0, -1) and (-1, 0), so it's fixed (we can find its equation). But since there are infinitely many parallel lines to line a, then each will have different y-intercept. Not sufficient.

(2 Line b passes through the point (10, 20).
[Reveal] Spoiler: OA

_________________

MGMAT CAT MATH http://gmatclub.com/forum/mgmat-cat-math-144609.html
MGMAT SC SUMMARY: http://gmatclub.com/forum/mgmat-sc-summary-144610.html

Last edited by Bunuel on 24 Apr 2012, 20:42, edited 1 time in total.
Edited the question
Manager
Status: I will not stop until i realise my goal which is my dream too
Joined: 25 Feb 2010
Posts: 235
Schools: Johnson '15
Followers: 2

Kudos [?]: 50 [3] , given: 16

Re: In the xy plane, line a and b have the same slope. [#permalink]

### Show Tags

24 Apr 2012, 20:39
3
KUDOS
monir6000 wrote:
In the xy plane, line a and b have the same slope. If the y intercept of line a is -1. What is the y-intercept of line b?
(1) the x-intercept of line a is -1
(2) line b passess through the point (10, 20)

given that line a and b are having the same slope... and given the line a y-intercept is -1...we need to find y-intercept of line b

1) x intercept of line a is -1

any line equation is given by y=mx+a for line a
y=mx+b for line b

hence the equation becomes y = mx - 1
for x intercept y becomes 0
0 = mx - 1
mx = 1

so for x intercept to be - 1 then to make that happen x = 1/m = -1
so m should be -1

but this makes the line b equation as y = -x + b

beyond this we cant find... hence not sufficient.. so A and D options are off...

2) line b passes through (10, 20)

y = mx + b

so 20 = 10m + b

two unknowns...we cannot solve

together.. we know that m = - 1 and 20 = 10m + b

so 20 = -10 + b
b = 30 which is the y-intercept of line b

hence C
_________________

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

Math Expert
Joined: 02 Sep 2009
Posts: 36618
Followers: 7103

Kudos [?]: 93594 [1] , given: 10579

Re: In the xy plane, line a and b have the same slope. [#permalink]

### Show Tags

24 Apr 2012, 20:46
1
KUDOS
Expert's post
1
This post was
BOOKMARKED
monir6000 wrote:
In the xy plane, line a and b have the same slope. If the y intercept of line a is -1. What is the y-intercept of line b?

(1) the x-intercept of line a is -1
(2) line b passess through the point (10, 20)

In the xy-plane, line a and line b have the same slope. If the y-intercept of line a is -1, what is the y-intercept of line b ?

You don't need any algebra or even drawing, to solve this question. Just try to visualize the info given. First of all notice that "line a and line b have the same slope" means that the lines are parallel.

(1) The x-intercept of line a is -1. We have two points of line a: (0, -1) and (-1, 0), so it's fixed (we can find its equation). But since there are infinitely many parallel lines to line a, then each will have different y-intercept. Not sufficient.

(2 Line b passes through the point (10, 20). We have one point of line a: (0, -1) and one point of line b: (10, 20). We can rotate two parallel lines around these points, which will give different y-intercept of line b. Not sufficient.

(1)+(2) We have fixed line a, and its parallel line b which passes through the point (10, 20), which means that line b is also fixed and we can find its y-intercept (through some particular point, you can draw only one line which will be parallel to some fixed line). Sufficient.

_________________
Manager
Joined: 27 May 2008
Posts: 126
Followers: 2

Kudos [?]: 66 [0], given: 4

Re: In the xy-plane, line a and line b have the same slope. [#permalink]

### Show Tags

25 Apr 2012, 07:16
Thanks for the quick explanation Bunuel. It takes less time using your method.
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13533
Followers: 577

Kudos [?]: 163 [0], given: 0

Re: In the xy-plane, line a and line b have the same slope. [#permalink]

### Show Tags

19 Aug 2016, 18:33
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: In the xy-plane, line a and line b have the same slope.   [#permalink] 19 Aug 2016, 18:33
Similar topics Replies Last post
Similar
Topics:
38 In the xy-plane, points A, B and C are not on the same line. 16 19 Jan 2013, 00:43
9 In the xy-plane, is the slope of line L greater than the 16 01 Feb 2012, 18:13
2 In the xy-plane, if line k has negative slope, is the 3 15 Apr 2011, 19:19
If k is a line in xy-plane, what is the slope of k? 3 28 Oct 2010, 07:58
If two lines have slopes a and b , respectively, are they 3 15 May 2010, 10:41
Display posts from previous: Sort by

# In the xy-plane, line a and line b have the same slope.

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.