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If k not equal to 0, 1 or -1 is 1/k>0? (1) 1/(k-1) >0 [#permalink]
 22 Oct 2006, 07:46
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If k not equal to 0, 1 or -1 is 1/k>0?
(1) 1/(k-1) >0
(2) 1/(k+1)>0
Any explanations will be appreciated.
Last edited by ishtmeet on 22 Oct 2006, 08:29, edited 1 time in total.
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I pick B
Since K>0 so 1/K>0
a. not suf, if K=- 0,5, equation holds true and K<0
b. suf, K has to be greater than 1
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For me (A),
k != -1,0,1
1/k>0 ?
NB: K could be any real numbers.
Stat1:
1/k-1 >0
<=> 1/k > 1 > 0
SUFF.
Stat2:
1/k+1 >0
<=> 1/k > -1
Pick numbers to be sure 
o k = -2, -1/2 > -1 and -1/2 < 0
o k = 2, 1/2 > -1 and 1/2 > 0
INSUFF.
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Intern
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Hey guys sorry for the confusion but it is 1/(k-1) and 1/(k+1). I have modified the question.
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ishtmeet wrote: Hey guys sorry for the confusion but it is 1/(k-1) and 1/(k+1). I have modified the question.
The question changes but my answer remain the same  It's still (A) for me
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If k not equal to 0, 1 or -1 is 1/k>0?
(1) 1/(k-1) >0
(2) 1/(k+1)>0
question is
is k<0
from one
k-1<0thus k< 1 could be a +ve fraction OR -VE .......not suff
from two
k+1<0 thus k <-1 thus ure k<0.......suff
my answer is B
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yezz wrote: If k not equal to 0, 1 or -1 is 1/k>0?
(1) 1/(k-1) >0
(2) 1/(k+1)>0
question is
is k<0
from one
k-1<0thus k< 1 could be a +ve fraction OR -VE .......not suff
from two
k+1<0 thus k <-1 thus ure k<0.......suff
my answer is B
Sorry Yezz, ... it should be for both bold > 0
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Why fig ......can you ellaborate
i believe if we have
1/x<0 we flip to x>0......wuts wrong in this
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yezz wrote: Why fig ......can you ellaborate
i believe if we have
1/x<0 we flip to x>0......wuts wrong in this
U cannot use the fonction f(x) = 1/x here.... we have 0 by right side
We have to use the properties of the operaiton "division"
Sign(1/x) < 0
<=> Sign(1)/Sign(x) <0
<=> Sign(x) < 0
or
1/x < 0
<=> x < 0 as 1 > 0
Last edited by Fig on 22 Oct 2006, 09:00, edited 1 time in total.
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st 1 says 1/(k-1)>0 that means k-1>0 that means k>1 that means k is +ve and thus 1/k>0 ... suff
st2 says 1/(k+1) >0 that means k+1>0 i.e k>-1 that means k can -ve fraction or k is positive . if k is -neg fraction 1/k <0 and if k is +ve 1/k >0 so insuff
Thus the answer is A.
What is the OA?
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Hi Guys,
The OA is A. Can anybody explain how did thi answer come??
As per the solutions given by folks since one says 1/(k-1) >0 it implies k-1 <0 or k<1 therefore K maybe greater that 0 0r less than 0. SO how come the correct answer is A in GMAT PREP.
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ishtmeet wrote: Hi Guys,
The OA is A. Can anybody explain how did thi answer come??
As per the solutions given by folks since one says 1/(k-1) >0 it implies k-1 <0 or k<1 therefore K maybe greater that 0 0r less than 0. SO how come the correct answer is A in GMAT PREP.
yogeshsheth did a great job on it
Stat1:
1/(k-1) >0
=> (k-1) > 0
<=> k > 1 > 0
=> 1/k > 0
SUFF
Stat2:
1/(k+1) >0
=> (k+1) > 0
<=> k > -1
=> 1/k < -1 or 1/k > 0
INSUFF
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Director
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Thanks Fig
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fig is this right or wrong why we did it your way??
eg: 1/x< 5 thus x>1/5
but if
1/x <0 we cant say x>1/0 because it is not defined ......right or wrong
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Director
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Correct yezz one can not take a reciprocal of inequality of type x<0
x<0 does not imply that 1/x >0 as 1/0 is not defined.
Hope that helps.
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yezz wrote: fig is this right or wrong why we did it your way??
eg: 1/x< 5 thus x>1/5
but if
1/x <0 we cant say x>1/0 because it is not defined ......right or wrong
Correct
The fonction f(x) = 1/x decreases when x inscreases but it's not defined when x = 0. Thus,
5 > 1
<=> f(5) < f(1) : the fonction decreases
<=> 1/5 < 1
Another example:
g(x)= x+1
The fonction g increases when x increases.
5 > 1
<=> g(5) > g(1) : the fonction increases
<=> 6 > 2
We flip when the function decreases when x increases
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Thanks yougish and Fig ......u saved my life 
I have a problem with iniqualities i dont know how to get over it
well i will keep trying and solving as much as i can
do u suggest any thing else i can do??
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yezz wrote: Thanks yougish and Fig ......u saved my life I have a problem with iniqualities i dont know how to get over it well i will keep trying and solving as much as i can do u suggest any thing else i can do?? U are welcome :D
Only thing, do not hesitate to come back to look some math basics ... but the most important is as u said: the practice
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Fig wrote: yezz wrote: Thanks yougish and Fig ......u saved my life I have a problem with iniqualities i dont know how to get over it well i will keep trying and solving as much as i can do u suggest any thing else i can do?? U are welcome :D Only thing, do not hesitate to come back to look some math basics ... but the most important is as u said: the practice Welcome yezz
Completely agree with you Fig practice helps in getting familiar in dealing with ineaualities
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yezz wrote: fig is this right or wrong why we did it your way??
eg: 1/x< 5 thus x>1/5
but if
1/x <0 we cant say x>1/0 because it is not defined ......right or wrong
Yes don't use the flip sign method when you have zero on the right side. In stead, think this way. For a product or ratio of two numbers to be positive, the two numbers have to have the same sign; for the product or ratio to be negative, the two numbers must have different signs.
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Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.
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