Solve for x, y
x=a
y=100-a
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2y+2a=200,y+x=100
To solve a pair of equations using substitution, first solve one of the equations for one of the variables. Then substitute the result for that variable in the other equation.
2y+2a=200
Pick one of the two equations which is more simple to solve for y by isolating y on the left hand side of the equal sign.
2y=200-2a
Subtract 2a from both sides of the equation.
y=100-a
Divide both sides by 2.
100-a+x=100
Substitute 100-a for y in the other equation, y+x=100.
x=a
Subtract 100-a from both sides of the equation.
y=100-a,x=a
The system is now solved.
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