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ganesh prasath: Junior | Next Rank: 30 Posts; Posts: 14; Joined: Sun Sep 12, 2010 9:09 pm

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by ganesh prasath » Sun Jun 05, 2011 4:46 am

If ax + b = 0, is x > 0?
a. a + b > 0
b. a - b > 0

in this question wont we b able to deduce the value of x from stmt 2 ?? as from stmt 2 we get to knw that a is a +ive no so x should also be +ive ...but the answer is E. Please explain

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Source: Beat The GMAT — Problem Solving | Sun Jun 05, 2011 4:46 am

cans: Legendary Member; Posts: 1309; Joined: Mon Apr 04, 2011 5:34 am; Location: India; Thanked: 310 times; Followed by:123 members; GMAT Score:750

by cans » Sun Jun 05, 2011 5:02 am

x>0??
ax+b=0
a) a+b>0
case1: a,b>0 then x<0 (to make ax+b=0)
case2: a<0,b>0 (b large enough to make a+b>0)
x>0 to make ax+b=0
Thus insufficient.
b)a-b>0
a>b ; a>-ax -> a(1+x)>0
if a>0, 1+x>0 or x>-1. thus x can be 0 or 2 (insufficient)

a&b together. add both 2a>0 or a>0
ax+b=0
case1: x=b=0
case2 : x=4/5,a=5,b=-4
Insufficient
IMO E

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sunilramu: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Thu Feb 24, 2011 4:47 am; Thanked: 1 times

by sunilramu » Sun Jun 05, 2011 7:05 am

1. a+b>0
a=1, b= 1, x = -1 satisfies ax+b = 0
a=-1, b=2, x=2 satisfies ax+b=0
Not Sufficient.

2. a-b>0
a=2, b=1, x=-0.5 satisfies ax+b=0
a=3, b=-1.5, x=0.5 satisfies ax+b=0
Not Sufficient.

1. & 2.
Samples in 2 also apply here.

Not Sufficient.

IMO E