BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Equation of a line

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
Legendary Member
Posts: 576
Joined: Sat Mar 13, 2010 8:31 pm
Thanked: 97 times
Followed by:1 members

by liferocks » Wed May 19, 2010 9:30 am
if point (r,s) is on y=3x+2 ..3r+2-s=0

From 1
either ( 3r+2-s)=0 or (4r+9-s)=0...not sufficient

From 2
either ( 3r+2-s)=0 or (4r-6-s)=0...not sufficient

combining
( 3r+2-s)=0....sufficient

Ans option C
"If you don't know where you are going, any road will get you there."
Lewis Carroll
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 362
Joined: Fri Oct 02, 2009 4:18 am
Thanked: 26 times
Followed by:1 members

by indiantiger » Wed May 19, 2010 9:33 am
It has been solved here:

https://www.beatthegmat.com/gmat-prep-ds-t3852.html
Top
User avatar
GMAT Instructor
Posts: 1052
Joined: Fri May 21, 2010 1:30 am
Thanked: 335 times
Followed by:98 members

by Patrick_GMATFix » Fri May 21, 2010 10:44 am
the Q tests your understanding that point (r,s) can belong to the line only if its coordinates fit the equation of the line. In other words we can rephrase this from "is (r,s) on line y=3x+2?" to "Is s=3r+2?"

This Q tests your understanding that the solution of a factored equation that is set to 0 is whatever values will make each factor 0. For instance, statemetn (1) tells us that (3r+2-s)(4r+9-s) = 0. This means that
a. 3r+2-s = 0 --> s=3r+2, or
b. 4r+9-s=0 --> s=4r+9

Since we don't know which is correct, we cannot answer the rephrase. Statement (2) will work the same way. Only when you merge the statements can you definitively know that s=3r+2. The correct answer is C

You can see a video of this solution for a step by step demo; this is QID 1088

-Patrick
Top
Post new topic Post Reply
• Page 1 of 1