is 1/k > 0?

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vzzai: Senior | Next Rank: 100 Posts; Posts: 85; Joined: Tue Sep 02, 2008 12:13 am; Thanked: 1 times; GMAT Score:650

by vzzai » Fri Nov 25, 2011 9:50 pm

If k is not equal to 0, 1, or -1, is 1/k > 0?

(1)1/(k+1)> 0

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

Unconfirmed OA is D. I went for A. Please explain.

Thank you,
Vj

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Source: Beat The GMAT — Data Sufficiency | Fri Nov 25, 2011 9:50 pm

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Fri Nov 25, 2011 11:36 pm

1/k will be > 0, when k is +ve.

Statement 1:

1/(k+1) > 0

This condition satisfies for all values of k>1.

But, condition also satisfies when k = -1/2. k can be +ve or -ve - Insufficient

Statement 2:

1/(k-1) > 0

k can take any value > 1 to satisfy this condition. (Given k cannot be 1)
Thus k should be +ve and > 1. Sufficient.

Answer should be B IMO. Note : Question does not mention k is an integer.

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vzzai: Senior | Next Rank: 100 Posts; Posts: 85; Joined: Tue Sep 02, 2008 12:13 am; Thanked: 1 times; GMAT Score:650

by vzzai » Sat Nov 26, 2011 2:36 am

I agree with you shankar.ashwin. I took K as integer! .

Thank you,
Vj

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Sat Nov 26, 2011 6:42 am

vzzai wrote:If k is not equal to 0, 1, or -1, is 1/k > 0?

(1)1/(k+1)> 0

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

Unconfirmed OA is D. I went for A. Please explain.

"1/k > 0" means exactly the same thing as "k > 0". Similarly, 1/(k+1) > 0 just means that k + 1 > 0, or that k > -1. So Statement 1 is not sufficient. Since 1/(k-1) > 0 just means that k - 1 > 0, or that k > 1, Statement 2 is sufficient.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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