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put this solution on YOUR website!Let x = the first number
Let y = the second number
Let x + y = 21
Let x - y = 3
I'll show you two strageties for solving this.
1) The first is the method of addition: add the equations together to eliminate a variable.
2) The second is the method of substitution: solve one of the equations in terms of one variable and and plug in or substitute that expression into the other equations.
Having more than one strategy to solve a problem allows for more flexibility in your approach!
Method of addition:
1) Add the two equations together. Note that each of the y terms cancel each other out. Combine like terms:
+
2)
3)
Divide both sides by 12
4)
Pick one of the given equations and solve for y by substituting your answer for x.
5)
Subtract 12 from both sides
6)
Check your answers by substituting into the other equation.
This checks out
The solution is:
Method of substitution:
Let x = the first number
Let y = the second number
Let x + y = 21
Let x - y = 3
1) Select one of the equations and solve for one of the variables (Let's solve our second equation for x}}}
Add y to both sides
2) Substitute this expression for x in the other equation
3) Solve for y:
Combine like terms
Subtract 3 from both sides
Divide both sides by 2
4) Substitute this solution for y and solve for x:
5) Check your answers by substituting your into the other equation:
This checks out
The solution is:
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