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Is (x + 1)/(x - 3) < 0 ?

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Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 11 Feb 2011, 01:57
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Is (x + 1)/(x - 3) < 0 ?

(1) -1 < x < 1
(2) x^2 - 4 < 0
[Reveal] Spoiler: OA

Last edited by Bunuel on 10 May 2013, 00:23, edited 1 time in total.
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Re: data suff inequalities [#permalink] New post 11 Feb 2011, 04:30
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Let p=(x+1)/(x-3)<0

Statement 1:
-1<x<1
So Range of p is between 0 and -1
Therefore, p is less than 0.
Sufficient.

Statement 2:
x^2-4 < 0
x^2 < 4
Take sq. rt. on both sides:
|x| < 2

=> -2<x<2
1/5<p<-3 [Range]
So we cannot say if p is less than 0
In Sufficient!

Ans A
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Re: data suff inequalities [#permalink] New post 11 Feb 2011, 06:44
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Lolaergasheva wrote:
Is x+1/x-3<0 ?

1) -1 < x < 1
2) x^2-4 < 0


Lolaergasheva, please format the questions properly:

Question should read:

Is (x+1)/(x-3)<0 ?

Is \(\frac{x+1}{x-3}<0\)? --> roots are -1 and 3, so 3 ranges: \(x<-1\), \(-1<x<3\) and \(x>3\) --> check extreme value: if \(x\) some very large number then \(\frac{x+1}{x-3}=\frac{positive}{positive}>0\) --> in the 3rd range expression is positive, then in 2nd it'll be negative and in 1st it'll be positive again: + - +. So, the range when the expression is negative is: \(-1<x<3\).

Thus the question basically becomes: is \(-1<x<3\)?

(1) -1 < x < 1. Sufficient.
(2) x^2-4 < 0 --> \(-2<x<2\). Not sufficient.

Answer: A.

Check for more about the approach used here: everything-is-less-than-zero-108884.html?hilit=extreme#p868863, here: inequalities-trick-91482.html and here: xy-plane-71492.html?hilit=solving%20quadratic#p841486

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Re: data suff inequalities [#permalink] New post 17 Mar 2011, 21:19
Another easy way to solve this problem...
1) -1<x<1
Plug in 1/2 and -1/2 in original statement, you will see that it is always negative.
2)-2<x<2
-3/2 gives you a positive value...hence not sufficient.

A
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Re: data suff inequalities [#permalink] New post 03 Aug 2011, 23:24
picking numbers here was short and precise:

S2-start with 1.5 (the answer is yes) and -1.5 (the answer is no). SO NS
S1- 0.5 AND -0.5 the answer is yes in both.though, picking numbers in is risky.
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Re: data suff inequalities [#permalink] New post 07 Aug 2011, 02:59
Bunuel, thanks for the explanation. +1+1
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Re: Is x+1/x-3<0 ? 1) -1 < x < 1 2) x^2-4 < 0 [#permalink] New post 10 Jan 2012, 13:50
This one's a thing of beauty.

NOTE: No property mentioned about x, so can't cross-multiply the inequality.
RULE1: If positive, cross-mutiply sign does not change
RULE2: If negative, cross-mutiply sign changes

1. This means that x is + or - fraction. Substituting gives us that the inequality will hold true for all fractions of x, both + or -. Suff.
2. x^2 - 4 < 0 => x^2 < 4 => x < 2 or x > -2. If x = 1.5, inequality holds true. If x = -1.5, it does not. Insuff.

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Re: Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 26 Sep 2013, 17:42
This may be a dumb question- but I thought on the GMAT that all square roots of positive integers are considered positive. Hence, B would be sufficient because it is assumed that x could only be positive 2.?? Help. When should I use that rule?
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Re: Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 27 Sep 2013, 00:34
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TAL010 wrote:
This may be a dumb question- but I thought on the GMAT that all square roots of positive integers are considered positive. Hence, B would be sufficient because it is assumed that x could only be positive 2.?? Help. When should I use that rule?


First of all notice that we have x^2-4<0 (-2<x<2) not x^2-4=0 (x=-2 or x=2).

Next, when the GMAT provides the square root sign for an even root, such as \(\sqrt{x}\) or \(\sqrt[4]{x}\), then the only accepted answer is the positive root. That is, \(\sqrt{25}=5\), NOT +5 or -5.

In contrast, the equation \(x^2=25\) has TWO solutions, +5 and -5. Even roots have only non-negative value on the GMAT.

Hope it helps.
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Re: data suff inequalities [#permalink] New post 07 May 2014, 23:15
Bunuel wrote:


Thus the question basically becomes: is \(-1<x<3\)?

(1) -1 < x < 1. Sufficient.
(2) x^2-4 < 0 --> \(-2<x<2\). Not sufficient.

Answer: A.

Hi Bunuel thanks for the above explaination and answer.

I have a doubt though, for 2nd statement possible regions are x<-2,-2<x<2 and x>2. and the signs come to +,-,+ so we selected middle one for the answer here. But will it be possible that more than one regions satisy the inequality? If yes then what should we do?
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Re: data suff inequalities [#permalink] New post 07 May 2014, 23:40
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aniketb wrote:
Bunuel wrote:


Thus the question basically becomes: is \(-1<x<3\)?

(1) -1 < x < 1. Sufficient.
(2) x^2-4 < 0 --> \(-2<x<2\). Not sufficient.

Answer: A.

Hi Bunuel thanks for the above explaination and answer.

I have a doubt though, for 2nd statement possible regions are x<-2,-2<x<2 and x>2. and the signs come to +,-,+ so we selected middle one for the answer here. But will it be possible that more than one regions satisy the inequality? If yes then what should we do?


No,There will be no other region satisfying the inequality. You can try and putting in values of the x<-2 and x>2 and see it for yourself.
Consider x=-50 or x=50...There is only 1 range where the inequality holds true.

Check out the solution for a similar question and look at graphical representation to understand how to handle such questions

if-x-is-an-integer-what-is-the-value-of-x-1-x-2-4x-94661.html
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Re: data suff inequalities [#permalink] New post 08 May 2014, 04:09
WoundedTiger wrote:
aniketb wrote:
Bunuel wrote:


Thus the question basically becomes: is \(-1<x<3\)?

(1) -1 < x < 1. Sufficient.
(2) x^2-4 < 0 --> \(-2<x<2\). Not sufficient.

Answer: A.

Hi Bunuel thanks for the above explaination and answer.

I have a doubt though, for 2nd statement possible regions are x<-2,-2<x<2 and x>2. and the signs come to +,-,+ so we selected middle one for the answer here. But will it be possible that more than one regions satisy the inequality? If yes then what should we do?


No,There will be no other region satisfying the inequality. You can try and putting in values of the x<-2 and x>2 and see it for yourself.
Consider x=-50 or x=50...There is only 1 range where the inequality holds true.

Check out the solution for a similar question and look at graphical representation to understand how to handle such questions

if-x-is-an-integer-what-is-the-value-of-x-1-x-2-4x-94661.html


Thanks woundedtiger, Its quite helpful. :thumbup: Its only one region then,until some exception comes..;)
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Re: Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 10 Jul 2014, 00:21
Hi Bunuel,

i have a doubt . In your first explanation above , you have written - frac{x+1}{x-3}<0? --> roots are -1 and 3.

How are roots -1 & 3 for this inequality .

Thanks in advance .

Kunal .
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Re: Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 16 Jul 2014, 22:02
Hello Bunuel,

if in stmt (1) -1<x-1 couldn't x be = 0 and hence answer E?
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Re: Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 17 Jul 2014, 07:18
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Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 04 Oct 2014, 19:09
Interesting question. Below is my solution.
(x+1)/(x-3) < 0
Y if x+1 > 0 and (x-3) < 0

A

(1)
-1 < x < 1
0 < x+1 < 2
-4 < x-3 < -2
Signs of both x+1 and x-3 will be opposite, so sufficient.

(2)
x^2 < 4
|x| < 2
-2 < x < 2
-1 < x+1 < 3
-5 < x-3 < -1
(x+1)/(x-3) does not have a consistent sign, so insufficient.
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Is (x + 1)/(x - 3) < 0 ? [#permalink] New post 03 Feb 2015, 17:13
Bunuel wrote:
Moved to DS subforum.

Lolaergasheva wrote:
Is x+1/x-3<0 ?

1) -1 < x < 1
2) x^2-4 < 0


Lolaergasheva, please format the questions properly:

Question should read:

Is (x+1)/(x-3)<0 ?

Is \(\frac{x+1}{x-3}<0\)? --> roots are -1 and 3, so 3 ranges: \(x<-1\), \(-1<x<3\) and \(x>3\) --> check extreme value: if \(x\) some very large number then \(\frac{x+1}{x-3}=\frac{positive}{positive}>0\) --> in the 3rd range expression is positive, then in 2nd it'll be negative and in 1st it'll be positive again: + - +. So, the range when the expression is negative is: \(-1<x<3\).

Thus the question basically becomes: is \(-1<x<3\)?

(1) -1 < x < 1. Sufficient.
(2) x^2-4 < 0 --> \(-2<x<2\). Not sufficient.

Answer: A.

Check for more about the approach used here: everything-is-less-than-zero-108884.html?hilit=extreme#p868863, here: inequalities-trick-91482.html and here: xy-plane-71492.html?hilit=solving%20quadratic#p841486

And again:

!
Please post PS questions in the PS subforum: gmat-problem-solving-ps-140/
Please post DS questions in the DS subforum: gmat-data-sufficiency-ds-141/

No posting of PS/DS questions is allowed in the main Math forum.


Dear Bunuel, in the above question you say that and I know that you got this result from x+1<0 so X<-1. However ,

in X>3 does you got it from that X-3>0 as aresult X > 3. My question is, does always the numerator for take

the same sign that in the question for example as above questin ( < ) and the denominator take the opposite

sign ( > )that in the question . If the answer is not so how you got X>3?
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Is (x + 1)/(x - 3) < 0 ?   [#permalink] 03 Feb 2015, 17:13
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