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DS - a - b > 0

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DS - a - b > 0

by Xbond » Wed Aug 26, 2009 10:06 am
Hi there,

Could you explain in the simplest this concept and how to resolve it


Is a - b > 0 ?
(1) a(square) = 16
(2) b(square) = 4
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Source: — Data Sufficiency |
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by JJJooe » Wed Aug 26, 2009 3:41 pm
difficult to understand the question...
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by beatthegmat » Wed Aug 26, 2009 3:48 pm
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by JJJooe » Wed Aug 26, 2009 4:04 pm
to know whether a>b requires that we know relation between both of them

(1)(2)TOGETHER
a=4 or -4
b=2 or -2

obviously，when a=4, a>b
but when a=-4,a<b

so insufficient

choose E
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Re: DS - a - b > 0

by shahdevine » Wed Aug 26, 2009 6:13 pm
Xbond wrote:Hi there,

Could you explain in the simplest this concept and how to resolve it


Is a - b > 0 ?
(1) a(square) = 16
(2) b(square) = 4
rewrite:

is a>b?

s1) a^2=16 --> a=-4 or 4 but we know nothing about b. insufficient.
s2) b^2=4 --> b=-2 or 2 but we know nothing about a.
insufficient
s1+s2) a>b when a=4 and b=2 or -2 however a could equal -4 which would invalidate a>2. In any case, with a and b having a range of values, s1+s2 is insufficient. therefore E.

you got this man!
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