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DS - POSITIVE INTEGER (m04q17) [#permalink]
 03 Sep 2008, 14:34
Question Stats:
43% (01:13) correct
56% (00:20) wrong based on 1 sessions
Is integer R positive? 1. R^3 = R2. |R| = RSource: GMAT Club Tests - hardest GMAT questions
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 14:36
B
from 1 : two possibilities -1,1
from 2 : has to be +ve else not possible
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 14:38
Again E.
1) R=0 or R=+-1
2) R=0 or Any positive #, including 1
1+2) still R=0 or R=1 So E.
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 14:52
IMO E.
At 1st I thought it will be B, but ya if R=0, that screws up evrything..
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 17:15
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Hmm I am getting B for this. This is Yes/No DS and a No answer is sufficient
We all agree on A is insuff. R ^ 3 - R = 0, which means R =0, 1 ,-1 ( No, Yes, No for the Q Is R +ve? ) hence Insuff
B is saying
R = R and -R = R (R is integer)
Lets say R =1 -R = -1 which is not equal to R same thing for any -ve integer
The only number I can think of satisfying the above two equations is 0
Is 0 positive? No ( neither positive nor negative) . Hence B.
Do you agree? Did I go wrong any where?
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 18:00
|R|=R means R=R when ris +ve and R=-R, when R is -ve
so, option gives you all the +ve integers + 0
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 19:16
I'm getting E for this problem as well.
(1) R could be negative, zero, or even positive.
(2) R could be positive or zero.
(1&2) R could still be positive or Zero
So our answer is E.
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 20:16
Yeap E is the answer! Thanks for discussion. I chose B making another stupid mistake.. considered "zero" as +ve.. RULE IS "ZERO is neither positive nor negative"
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 21:04
K! Seriously I need some enlightenment as I am totally lost here.
When I see a absolute variable I create 2 equations and we are given that R is integer and | R | = R
I read it as Can you find integer(s) such that R = R and -R = R
For all integers positive and negative I can say R is not equal to -R except for 0
0 is the integer that satisfies both R = R and -R = R
0 is neither +ve nor -ve. Going back to the Q Is R positive? NO
I felt that its sufficient and chose B.
Can some one explain where I am going wrong?
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 21:11
icandy wrote: K! Seriously I need some enlightenment as I am totally lost here.
When I see a absolute variable I create 2 equations and we are given that R is integer and | R | = R
I read it as Can you find integer(s) such that R = R and -R = R
For all integers positive and negative I can say R is not equal to -R except for 0
0 is the integer that satisfies both R = R and -R = R
0 is neither +ve nor -ve. Going back to the Q Is R positive? NO
I felt that its sufficient and chose B.
Can some one explain where I am going wrong? |R|=R one solution for this is R=0 other solutions when R>0 R=R So R is +ve when R<0 R=-R --> invalid so R can't be -ve So all together two solutions R=0 or R is +ve Is R Positive? No when R=0 Is R Positive? Yes when R is +ve insuffcient.
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 21:33
x2suresh wrote: icandy wrote: K! Seriously I need some enlightenment as I am totally lost here.
When I see a absolute variable I create 2 equations and we are given that R is integer and | R | = R
I read it as Can you find integer(s) such that R = R and -R = R
For all integers positive and negative I can say R is not equal to -R except for 0
0 is the integer that satisfies both R = R and -R = R
0 is neither +ve nor -ve. Going back to the Q Is R positive? NO
I felt that its sufficient and chose B.
Can some one explain where I am going wrong? |R|=R one solution for this is R=0 other solutions when R>0 R=R So R is +ve when R<0 R=-R --> invalid so R can't be -ve So all together two solutions R=0 or R is +ve Is R Positive? No when R=0 Is R Positive? Yes when R is +ve insuffcient. Now I see what I am doing differently. When I look at |R| = R and consider the two equations I am considering that both the cases of R = R and R = -R needs to be satisfied. What needs to be checked is whether I arrive at same answer in all three cases. Thanks.
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 21:44
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Re: DS - POSITIVE INTEGER [#permalink]
03 Sep 2008, 23:57
Good posting x2suresh.....one new thing that I have learnt is that in such problems, always cross check with substitution.....
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Re: DS - POSITIVE INTEGER (m04q17) [#permalink]
24 Jul 2010, 05:25
Yep. Answer is E. The rule tested here is: 0 is neither +ve nor -ve
Cheers!
Ravi
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Re: DS - POSITIVE INTEGER (m04q17) [#permalink]
28 Jul 2011, 06:32
Simply test +1, -1, and 0 here to get answer. E
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Re: DS - POSITIVE INTEGER (m04q17) [#permalink]
29 Jul 2011, 18:05
E is the answer....0 is neither +ve nor -ve
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Re: DS - POSITIVE INTEGER (m04q17) [#permalink]
31 Jul 2012, 12:06
Seemed really easy to lead to B. I made the silly mistake and did not consider 0 for the statement (ii). Realized my mistake and learnt from it.
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Re: DS - POSITIVE INTEGER (m04q17) [#permalink]
31 Jul 2012, 21:48
is it something like /0/ does not exist or the value of /0/ is again a zero which is neither positive nor negative???
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Re: DS - POSITIVE INTEGER (m04q17) [#permalink]
02 Aug 2012, 00:53
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Re: DS - POSITIVE INTEGER (m04q17)
[#permalink]
02 Aug 2012, 00:53
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