Weird Data Sufficiency

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MonicaKhan: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Fri Apr 06, 2007 8:14 pm

by MonicaKhan » Sun Apr 22, 2007 7:16 am

Here's a Data Sufficiency question from the GMATPrep software that I can't figure out the answer to:

In the x-y plane, does the line with equation y = 3x + 2 contain the point (r,s)?

(1) (3r + 2 - s)(4r +9 - s) = 0
(2) (4r - 6 - s)(3r + 2 - s) = 0

I think each of these statements are sufficient to answer the question, but the answer is supposedly C. Not sure why, so any insights would be greatly appreciated. Thanks!

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Source: Beat The GMAT — Data Sufficiency | Sun Apr 22, 2007 7:16 am

jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

Re: Weird Data Sufficiency

by jayhawk2001 » Sun Apr 22, 2007 8:36 am

MonicaKhan wrote:Here's a Data Sufficiency question from the GMATPrep software that I can't figure out the answer to:

In the x-y plane, does the line with equation y = 3x + 2 contain the point (r,s)?

(1) (3r + 2 - s)(4r +9 - s) = 0
(2) (4r - 6 - s)(3r + 2 - s) = 0

I think each of these statements are sufficient to answer the question, but the answer is supposedly C. Not sure why, so any insights would be greatly appreciated. Thanks!

1 - insufficient. We know (3r + 2 -s = 0) OR (4r + 9 - s = 0).

2 - insufficient. We know (4r - 6 - s = 0) OR (3r + 2 - s = 0)

1 and 2 together are sufficient.

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MonicaKhan: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Fri Apr 06, 2007 8:14 pm

by MonicaKhan » Sun Apr 22, 2007 12:59 pm

Duh, I don't know how I missed that. Thanks for the clarification!

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Prasanna: Master | Next Rank: 500 Posts; Posts: 418; Joined: Mon Feb 26, 2007 6:41 pm; Thanked: 24 times

by Prasanna » Mon Apr 23, 2007 5:23 am

Sorry, I am not able to understand why it would be C. From (1) and (2) we have two equations in each, which can be solved to answer the question.

What is that I am missing here? Would be grateful if you could explain.

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ronniecoleman: Legendary Member; Posts: 546; Joined: Sun Nov 16, 2008 11:00 pm; Location: New Delhi , India; Thanked: 13 times

by ronniecoleman » Thu Dec 18, 2008 1:34 am

IMO C
1 let (3r + 2 - s) = K
(4r +9 - s) = L
(4r - 6 - s) = P

K*L = 0
K*P = 0

Now if K ! =0 Then L = P =0
but they (4r - 6 - s) != )(4r +9 - s) ( on any day they are not equal )

hence K =0

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