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Number properties

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Number properties

by Pedros » Wed Sep 09, 2009 10:08 am
if |x| - |y| = |x+y| and xy not equal zero , which of the following must be true ?

a) x-y> 0
b) x-y< 0
c) x+y> 0
d) xy> 0
e) xy< 0

need to know whether there is a rule i am missing or a startegy to solve this one.

answer is E

Thanks
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by georgeung » Wed Sep 09, 2009 10:30 am
I need a better strategy, too. I came down with A, C, and E and knew E had to be true because X and Y had to be opposite charges, but I couldn't rule out A or C.
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by PussInBoots » Sat Sep 12, 2009 6:02 pm
The answer is E. x and y has to be opposite signs, hence E is always correct.
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by Nermal » Sun Sep 13, 2009 1:52 am
I tried all the possible outcomes for this equation.

There are 8 different combinations of positive and negative values of |x|-|y|=|x+y|

You only get two that are not zeros.

x+y=-x-y => xy=-1

-x-y=x+y => xy=-1

Therefore: xy<0 (E)

But this way takes too long, maybe someone can show a quicker way of solving this kind of problem.
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Re: Number properties

by fruti_yum » Tue Sep 15, 2009 12:22 pm
Pedros wrote:if |x| - |y| = |x+y| and xy not equal zero , which of the following must be true ?

a) x-y> 0
b) x-y< 0
c) x+y> 0
d) xy> 0
e) xy< 0

need to know whether there is a rule i am missing or a startegy to solve this one.

answer is E

Thanks
Need some help on this question.. experts pls help
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Re: Number properties

by umaa » Tue Sep 15, 2009 1:48 pm
Pedros wrote:if |x| - |y| = |x+y| and xy not equal zero , which of the following must be true ?

a) x-y> 0
b) x-y< 0
c) x+y> 0
d) xy> 0
e) xy< 0

need to know whether there is a rule i am missing or a startegy to solve this one.

answer is E

Thanks
IMO E.

I have got the answer by substituting numbers for X and Y

Substitute X = 5 and Y = -2, works -I

Substitute X = 2 and Y = 5, NO

Substitute X = -2, Y = 5, NO

Substitute X = -5, Y = 2, WORKS

For |X| - |Y| = |X-Y| and XY nt equal to 0, |X| should be higher than |Y|.

OF all the answer choices, E only satisfies the condition.

Hope it helps.
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by viju9162 » Tue Sep 15, 2009 10:34 pm
yes, E satisfies the answer. Either X or Y should be -ve to satisfy the equation..
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