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equations

by Gurpinder » Wed Sep 15, 2010 11:09 am
What is the value of b + c ?
(1) ab + cd + ac + bd = 6
(2) a + d = 4

[spoiler]oa: (C)[/spoiler]


[spoiler]the first one can be factored to a(b+c)+d(c+b)=6

does this mean that (a+d)+(c+b)=6???

and then simply plugin the value from (2) ???[/spoiler]


please explain!

thx.
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by tpr-becky » Wed Sep 15, 2010 11:43 am
you are correct that the first one can be factored to a(b+c) + d(b+c)=6 but your second equation is incorrect. from the previous equation we can factor out a (b+c) to get (b+c)(a+d). but this still doesn't help becuase we don't know a+d.

left with BCE

STatement 2 doesn't give you enough information by iself becuase we still have b and c undefined. Left with C or E.

Together, after the equation from statement one is factored we get (b+c)(a+d)=6 and (a+d)=4 which means (b+c)(4)=6 and from there we can solve it which means this is sufficient.

choose C.
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by Gurpinder » Wed Sep 15, 2010 11:53 am
Thx Becky!
"Do not confuse motion and progress. A rocking horse keeps moving but does not make any progress."
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