is x^3 > y?

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Mon Mar 12, 2012 2:44 am

If x and y are positive, is x^3 > y?
(1) âˆšx > y.
(2) x > y.

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Source: Beat The GMAT — Data Sufficiency | Mon Mar 12, 2012 2:44 am

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Mon Mar 12, 2012 6:23 am

sanju09 wrote:If x and y are positive, is x^3 > y?
(1) âˆšx > y.
(2) x > y.

(1) âˆšx > y
If x = 4, y = 1, then 2 > 1 and x^3 = 4^3 = 64 > 1. Here x^3 > y.
If x = 1/4, y = 1/3, then 1/2 > 1/3 and x^3 = 1/64. Here x^3 < y.
No definite answer; NOT sufficient.

(2) x > y
If x = 4, y = 1, then 4 > 1 and x^3 = 4^3 = 64 > 1. Here x^3 > y.
If x = 1/2, y = 1/3, then 1/2 > 1/3 and x^3 = 1/8. Here x^3 < y.
No definite answer; NOT sufficient.

Combining (1) and (2), If x = 4, y = 1, then âˆšx > y and x > y. Here x^3 > y.
If x = 9/16, y = 1/2, then âˆšx = 3/4. Here âˆšx > y and x > y. Here x^3 < y.
No definite answer; NOT sufficient.

The correct answer is E.

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killer1387: Legendary Member; Posts: 581; Joined: Sun Apr 03, 2011 7:53 amFollowed by: 5 members; Thanked: 52 times

by killer1387 » Mon Mar 12, 2012 6:26 am

IMO E

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Mon Mar 12, 2012 7:17 pm

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