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Mod problem - anything wrong with this approach

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Thu Nov 27, 2008 4:17 pm

Sris,
I think Pardeep did the same thing as u di but the oa seems to be E). I have included my thougths too. Look it over and provide your feedback.

Pradeep,
Whats the source and do they provide any explanation on why its E)?

Regards,
Cramya

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srisl11: Senior | Next Rank: 100 Posts; Posts: 72; Joined: Thu Nov 06, 2008 10:27 am; Location: Pittsburgh; Thanked: 4 times

by srisl11 » Thu Nov 27, 2008 4:38 pm

cramya wrote:Sris,
I think Pardeep did the same thing as u di but the oa seems to be E). I have included my thougths too. Look it over and provide your feedback.

Pradeep,
Whats the source and do they provide any explanation on why its E)?

Regards,
Cramya

I think the OA is wrong...If not I badly need the explanation

Lets say we have to find the value of x.

equation 1 is (x-1)(x-4) = 0
Then x can be either 1 or 4

equation 2 is x-1 != 0
THen x can take any value except 1

But x= 4 is the only value which will satisfy both the equations.
here IMO C not E

If this approach is wrong then probably I have to redo all the problems in equations and inequations

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Thu Nov 27, 2008 4:50 pm

You could be right also! I have PM'd Stuart and we will see how this turns out.

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Thu Nov 27, 2008 10:18 pm

austin wrote:Tryingmybest,

Statement 1: |x+1| = 2|x-1|
Squaring, (x+1)^2 = 4(x-1)^2
=>x^2+1+2x = 4x^2+4-8x
=> 3x^2-10x+3 = 0
=> 3x^2-9x-x+3 = 0
=> 3x(x-3) -1(x-3) = 0
=> (3x-1) (x-3) = 0

How do you get img. roots?

This is a great approach to this question. I agree that the answer is (C), since statement (2) elminates one of the two possible values for x, leaving you with the certainty that x = 1/3.

One note on saving some time. Once you arrived at:

3x^2-10x+3 = 0

you knew that statement (1) gave you two possible values for x, which is enough to say that (1) is insufficient by itself.

When we get to the combination stage (since (2) is clearly insufficient by itself), all we really care about is if x=3 is one of the solutions for statement (1). So, if you're not sure how to factor it, just try plugging in x=3. In this case it works, so we know that statement (2) eliminates one of the two solutions and that combined the statements are sufficient.

Even if we have no clue what the second solution is, knowing that x has only one possible value is all we need to prove sufficiency.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Thu Nov 27, 2008 10:23 pm

Thanks again Stuart for the explanation/clarification!

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