How do you solve x + y = 12 and y = 2x?

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Answer 1 · 2015-10-15T21:36:56

You can solve it like this:

We have 2 simultaneous equations:

#x+y=12" "color(red)((1))#

#y=2x" "color(red)((2))#

From #color(red)((1))# we can write:

#y=(12-x)#

Substituting this value of #y# into #color(red)((2))# gives:

#(12-x)=2x#

#12=3x#

#x=12/3=4#

Substituting this value of #x# into #color(red)((1))# gives:

#4+y=12#

#y=12-4#

#y=8#