inequality

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earth@work: Master | Next Rank: 500 Posts; Posts: 248; Joined: Mon Aug 11, 2008 9:51 am; Thanked: 13 times

by earth@work » Fri Feb 13, 2009 9:55 pm

If x is negative, is x < -3?
(1) x^2 > 9
(2) x^3 < -9
Ans: [spoiler]do not have correct answer with me, i guess it is D : 1)gives x<-3 & (2) gives -3<x<0 [/spoiler]

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Source: Beat The GMAT — Data Sufficiency | Fri Feb 13, 2009 9:55 pm

DanaJ: Site Admin; Posts: 2567; Joined: Thu Jan 01, 2009 10:05 amFollowed by: 550 members; Thanked: 712 times; GMAT Score:770

by DanaJ » Fri Feb 13, 2009 10:53 pm

1. makes for x < -3. Since x^2 > 9, this means that x is either greater than 3 or smaller than -3. But seen as how x < 0, then x < -3.
2. x^3 < -9 helps us establish that x^3 < -8, which means that x < -2. However, since x is not necessarily an integer, we cannot tell if indeed x is smaller than -3 or not. It could be -100 or -2.1.

I'd go with A on this one.

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naaga: Master | Next Rank: 500 Posts; Posts: 129; Joined: Mon Dec 15, 2008 11:43 pm; Location: Hyderabad; Thanked: 2 times

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by naaga » Sat Feb 14, 2009 7:38 am

ans should be A

stmt I is sufficient

why stmt II is not sufficient

if you take x= -3 x^3 is -27 , so sufficient which is <-9

but -3 is never < -3 , so, contradictory arises
Hence , B is insufficent
Ans must be (A)

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earth@work: Master | Next Rank: 500 Posts; Posts: 248; Joined: Mon Aug 11, 2008 9:51 am; Thanked: 13 times

by earth@work » Sat Feb 14, 2009 9:26 am

thanks, i was making careless error! It is A.
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