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Is xy < 4 ?

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Math Expert
Joined: 02 Sep 2009
Posts: 50001
Is xy < 4 ?  [#permalink]

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21 Mar 2017, 05:40
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100% (02:18) correct 0% (00:00) wrong based on 10 sessions

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Is xy < 4 ?

(1) x^2 + y^2 < 8
(2) x – y < 1

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Joined: 05 Mar 2015
Posts: 995
Re: Is xy < 4 ?  [#permalink]

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21 Mar 2017, 11:11
Bunuel wrote:
Is xy < 4 ?

(1) x^2 + y^2 < 8
(2) x – y < 1

(1) x^2 + y^2 < 8
x^2 + y^2 -2xy < 8-2xy
(x-y)^2 < 2(4-xy)
since (x-y)>=0
thus
2(4-xy)>0
or 4>xy
suff

(2) if x=3 , y= 2.5 ....xy>4
but if x=y=1 then xy<4
insuff

Ans A
Re: Is xy < 4 ? &nbs [#permalink] 21 Mar 2017, 11:11
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