OG11 DS# 146

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anaitalt: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Fri Jun 05, 2009 7:08 am

by anaitalt » Sun Nov 15, 2009 3:25 am

(pg 290)

Is n an integer?

(1) n^2 is an integer
(2) n^(1/2) is an integer

Can anyone please give better reasoning than the OG?

Thanx

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Source: Beat The GMAT — Data Sufficiency | Sun Nov 15, 2009 3:25 am

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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

Re: OG11 DS# 146

by Ian Stewart » Sun Nov 15, 2009 3:10 pm

anaitalt wrote:(pg 290)

Is n an integer?

(1) n^2 is an integer
(2) n^(1/2) is an integer

Can anyone please give better reasoning than the OG?

Thanx

Statement 1: n^2 = z, where z is an integer. So n = Â±sqrt(z). Well, if z=2 then n is not an integer, while if z=1, n is an integer. Not sufficient.

Statement 2: sqrt(n) = z, where z is an integer. So n = z^2, and n is the square of an integer, so must be an integer. 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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