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Is k > 0?

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Is k > 0?

by mehravikas » Wed Jun 11, 2008 3:45 am
S10-7 If -10 < k <10> 0?

(1) 1/k > 0
(2) k^2 > 0

OA is 'A', but shouldn't the answer be 'D', as we never have something like -0.

Please explain.
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by saege » Wed Jun 11, 2008 9:15 am
Assuming you Q is this:

If -10<k<10>0?

It says K lies between -10 and 10 then looking at the statements

1. 1/K >0 there is only 1 value of K that makes 1/k >than 0 that is K= 1 and as per the condition k >0.

2. k^2>0

Plug in values

K^2 K Is K>0
4 2 Yes
4 -2 no

So we have a yes and no answer therefore it is not sufficient.

Then ans is A
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by Stuart@KaplanGMAT » Wed Jun 11, 2008 12:40 pm
Always a good idea to click the "disable html in this post" box below the text box (html uses < and > for tags so if you have html enabled it will mess up inequalities).

You can also go right into "My Profile" and disable it permanently.
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by mehravikas » Fri Jun 13, 2008 4:30 am
Thanks for the solution. The original question was - -10 < k < 10, is k > 0?

Mostly in DS questions, we get something like, what is the value of x, given that x^2 > 4.

We cant find a solution to it because we assume, x > +2 or -2. I was thinking on the same terms for the equation k^2 > 0, and saying that k > +0 or -0 would be wrong.
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by anshul265 » Fri Jun 13, 2008 5:34 pm
I don't agree with "saege's" explaination for A.

i) When we have 1/k>0 it simply says that 1/k is positive. 1/k can also be a fraction example 1/2 for k=2 and it can be another whole number example 2 for k=0.5. But as we have 1/k positive, we know k is also positive. Sufficient.

ii) This says k^2>0 which means square of k is positive. But k could be both positive or negative. Insufficient.

Thus answer is A.

Follow this positive negative approach to save time as you wouldn't need to consider all possible cases.
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by Ian Stewart » Sat Jun 14, 2008 3:10 am
anshul's solution above is good- it correctly interprets the first statement, which tells you that k is positive, but no more than that (it does not give you a value for k).
mehravikas wrote: Mostly in DS questions, we get something like, what is the value of x, given that x^2 > 4.

We cant find a solution to it because we assume, x > +2 or -2.
If x^2 > 4, then we know that x > 2 or x < -2.
mehravikas wrote: I was thinking on the same terms for the equation k^2 > 0, and saying that k > +0 or -0 would be wrong.
No, you can look at this in the same way if you like. If k^2 > 0, then k > 0 or k < -0. But -0 is just 0. So if you know k^2 > 0, you know that k > 0 or k < 0 -- in other words, this only tells you that k is not equal to zero. k could have any other value.
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