Math Expressions Worksheet With Answers - Grade 7 And 8 - University Of Waterloo - 2013 Page 8
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12Example
A system of equations looks like:
x + y = 20
(1)
2x
y = 7
(2)
We will use everything we have covered today, plus substitution, to solve this system.We
must find x and y such that both equations are satisfied.
Steps for Solving:
1. Pick an equation and solve for a variable of your choice in terms of the other variable.
2. Replace the variable in the second equation with the expression found above.
3. Solve for the remaining variable in the equation and substitute that expression into
the initial equation you chose and solve for the last variable.
This will become more clear in the following example.
Example
x + y = 20
(1)
2x
y = 7
(2)
First, solve (1) for y.
x + y
x
= 20
x
y = 20
x
Now replace y in (2) with 20
x.
2x
(20
x) = 7
Solve this for x.
2x
(20
x)
= 7
2x
20 + x = 7
3x
20+20
=
7+20
3x
27
=
3
3
x = 9
8
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