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AustraliaVIC
VCE 11 General 2023

2.06 Practical problems

Lesson

Practical problems using linear and simultaneous equations

Simultaneous equations are incredibly useful for real life applications. They are used for problems that have at least two unknown quantities and at least two pieces of information involving both of these quantities.

How to solve a real life problem using simultaneous equations:

  1. Read the question entirely from start to finish.

  2. Assign variables to each unknown quantity (for example, let x be the number of \ldots)

  3. Use the information given in the question to develop simultaneous linear equations.

  4. Use either substitution, elimination or graphical methods to find solution to simultaneous equations.

  5. Answer the problem given in the question.

Examples

Example 1

The length of a rectangle is 12 units more than the width, and the perimeter of the rectangle is 56 units. Let y be the width and x be the length of the rectangle.

a

Use the fact that the length of the rectangle is 12 units more than the width to set up an equation for x and y.

Worked Solution
Create a strategy

Turn the following into a mathematical statement: The length is 12 more than the width.

Apply the idea
\displaystyle \text{length}\displaystyle =\displaystyle \text{width} + 12Write the equation in words
\displaystyle x\displaystyle =\displaystyle y+12Replace width with y and length with x
b

Use the fact that the perimeter of the rectangle is 56 units to set up an another equation for x and y.

Worked Solution
Create a strategy

Use the perimeter of a rectangle formula P=2x+2y.

Apply the idea
\displaystyle 2x+2y\displaystyle =\displaystyle PWrite the formula
\displaystyle 2x+2y\displaystyle =\displaystyle 56Substitute the perimeter
\displaystyle x+y\displaystyle =\displaystyle 28Divide both sides by 2
c

First solve for y to find the width.

Worked Solution
Create a strategy

Use the substitution method.

Apply the idea
\displaystyle x\displaystyle =\displaystyle y+12(1)
\displaystyle x+y\displaystyle =\displaystyle 28(2)
\displaystyle y+12+y\displaystyle =\displaystyle 28Substitute (1) into (2)
\displaystyle 2y+12\displaystyle =\displaystyle 28Add like terms
\displaystyle 2y\displaystyle =\displaystyle 16Subtract 12 from both sides
\displaystyle y\displaystyle =\displaystyle 8Divide both sides by 2
d

Now solve for x to find the length

Worked Solution
Create a strategy

Substitute the value of y found into equation 1.

Apply the idea
\displaystyle x\displaystyle =\displaystyle y+12(1)
\displaystyle x\displaystyle =\displaystyle 8+12Substitute y=8 into (1)
\displaystyle x\displaystyle =\displaystyle 20Evaluate
Idea summary

How to solve a real life problem using simultaneous equations:

  1. Read the question entirely from start to finish.

  2. Assign variables to each unknown quantity (for example, let x be the number of \ldots)

  3. Use the information given in the question to develop simultaneous linear equations.

  4. Use either substitution, elimination or graphical methods to find solution to simultaneous equations.

  5. Answer the problem given in the question.

Outcomes

U1.AoS4.8

solve linear equations constructed from word problems, including simultaneous linear equations

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