Taking Negative Sign in Modulus

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Uva@90: Master | Next Rank: 500 Posts; Posts: 490; Joined: Thu Jul 04, 2013 7:30 amFollowed by: 5 members; Location: Chennai, India; Thanked: 83 times

by Uva@90 » Thu Nov 14, 2013 9:50 pm

Hi All,
I have a doubt while handling Negative Sign with Absolute Values

Example:

|5x-3| - |3-4x| >0

Here Can I replace it with this,

|5x-3|+ |4x-3| >0
Is this allowed ?

Thanks in advance.

Regards,
Uva.

Known is a drop Unknown is an Ocean

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Source: Beat The GMAT — Problem Solving | Thu Nov 14, 2013 9:50 pm

theCodeToGMAT: Legendary Member; Posts: 1556; Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members; Thanked: 448 times; GMAT Score:650

by theCodeToGMAT » Thu Nov 14, 2013 10:10 pm

I don't think you can do so..

|3-4x| is interchange with |4x - 3|

but, we cannot extract "-ve" sign from Modulus.

Was this observation in some question? if so, can you please share the question

R A H U L

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[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Thu Nov 14, 2013 11:01 pm

Hi Uva@90,

It's important not to try to manipulate math concepts that you don't completely understand. It's far better to use the TESTing Values to define whatever patterns exist in the given information.

Here, we have:
|5X-3| - |3-4X| > 0

So let's just figure out whatever we can about permissible values that fit the given information:

Could X = 0? NO.
Could X = 1? YES.
Could X = -1? YES.

This means that "a shift" occurs somewhere around the value 0; this is the "hinge point" of the calculation and it's a piece of info that you can likely use to solve whatever question is attached to this info.

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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Uva@90: Master | Next Rank: 500 Posts; Posts: 490; Joined: Thu Jul 04, 2013 7:30 amFollowed by: 5 members; Location: Chennai, India; Thanked: 83 times

by Uva@90 » Fri Nov 15, 2013 1:47 am

theCodeToGMAT wrote:I don't think you can do so..

|3-4x| is interchange with |4x - 3|

but, we cannot extract "-ve" sign from Modulus.

Was this observation in some question? if so, can you please share the question

Thanks Rahul,

Actually I trying to solve the problem in the below link,
https://www.beatthegmat.com/pls-explain- ... 71749.html

I thought of finding the range of X. It could be easy for calculation if that's is possible, that's why

(Unfortunate

)

Regards,
Uva.

Known is a drop Unknown is an Ocean

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Uva@90: Master | Next Rank: 500 Posts; Posts: 490; Joined: Thu Jul 04, 2013 7:30 amFollowed by: 5 members; Location: Chennai, India; Thanked: 83 times

by Uva@90 » Fri Nov 15, 2013 1:49 am

[email protected] wrote:Hi Uva@90,

It's important not to try to manipulate math concepts that you don't completely understand. It's far better to use the TESTing Values to define whatever patterns exist in the given information.

Here, we have:
|5X-3| - |3-4X| > 0

So let's just figure out whatever we can about permissible values that fit the given information:

Could X = 0? NO.
Could X = 1? YES.
Could X = -1? YES.

This means that "a shift" occurs somewhere around the value 0; this is the "hinge point" of the calculation and it's a piece of info that you can likely use to solve whatever question is attached to this info.

GMAT assassins aren't born, they're made,
Rich

Thanks Rich.

not to try to manipulate math concepts that you don't completely understand. It's far better to use the TESTing Values to define whatever patterns exist in the given information.

Ha ha.. Sure. I won't.

Regards,
Uva.

Known is a drop Unknown is an Ocean

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theCodeToGMAT: Legendary Member; Posts: 1556; Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members; Thanked: 448 times; GMAT Score:650

by theCodeToGMAT » Fri Nov 15, 2013 1:51 am

Uva@90 wrote:
theCodeToGMAT wrote:I don't think you can do so..

|3-4x| is interchange with |4x - 3|

but, we cannot extract "-ve" sign from Modulus.

Was this observation in some question? if so, can you please share the question
Thanks Rahul,

Actually I trying to solve the problem in the below link,
https://www.beatthegmat.com/pls-explain- ... 71749.html

I thought of finding the range of X. It could be easy for calculation if that's is possible, that's why
(Unfortunate )

Regards,
Uva.

I could guess that

that's why I asked

R A H U L

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Mathsbuddy: Master | Next Rank: 500 Posts; Posts: 447; Joined: Fri Nov 08, 2013 7:25 amFollowed by: 1 member; Thanked: 25 times

by Mathsbuddy » Sat Nov 16, 2013 11:01 am

Uva@90 wrote:Hi All,
I have a doubt while handling Negative Sign with Absolute Values

Example:

|5x-3| - |3-4x| >0

Here Can I replace it with this,

|5x-3|+ |4x-3| >0
Is this allowed ?

Thanks in advance.

Regards,
Uva.

As |3-4x|=|4x-3|, then the answer is no. Modulus is just the value without any sign, therefore changing a sign inside the modulus bars, does not change it.

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