How do you solve 7x-y=447x−y=44 and x+4y=27x+4y=27 by elimination?

1 Answer
Simon Moore
Feb 14, 2017

Not sure what you mean by "elimination" but I do it this way.....

Explanation:

First, 7x - y = 447x−y=44 therefore 7x = 44 + y7x=44+y and x = (44 + y) / 7x=44+y7
Also, x + 4y = 27x+4y=27 therefore x = 27 -4yx=27−4y

Therefore 44 + y = 7.(27 - 4y)44+y=7.(27−4y)
And therefore 44 + y = 189 -28y44+y=189−28y by multiplying out the bracket.
So y + 28 y = 189 -44y+28y=189−44
And 29 y = 14529y=145
Therefore y =145/29= 5y=14529=5.

And we already know that x = 27 - 4yx=27−4y
So substituting in y we get x = 27 - (4.5) = 27 -20 = 7x=27−(4.5)=27−20=7.

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