02-06-2016
Mathematics

contestada

.07x+.09y=4000
x+y=404.2

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02-06-2016

times first equation by 100
7x+9y=400000

multiply second equation by -7
-7x-7y=-2829.4

add to other equation

7x+9y=400000
-7x-7y=2829.4 +
0x+2y=397170.6

2y=397170.6
divide by 2
y=198585.3
sub back

x+y=404.2
x+198585.3=404.2
minus 198585.3 both sides
x=-198181.1

(-198181.1, 198585.3)

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