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Year 10
Higher

Solving simultaneous equations by elimination from a context

I can solve two linear simultaneous equations given in context using elimination.

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New
New
Year 10
Higher

Solving simultaneous equations by elimination from a context

I can solve two linear simultaneous equations given in context using elimination.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. It is possible to find a solution that satisfies a problem with two unknowns by trial and error.
  2. It is possible to use the difference between the two scenarios to create a third valid scenario.
  3. Once you know one of the unknowns, you can substitute to find the other.

Common misconception

Subtracting the variables one way round but the constants the other way.

Pupils could rewrite their equations so the one they are subtracting is underneath in a column method. For this lesson, the answers are in context so pupils should spot when negative answers do not make sense.

Keywords

  • Simultaneous equations - Equations which represent different relationships between the same variables are called simultaneous equations.

  • Elimination - Elimination is a technique to help solve equations simultaneously and is where one of the variables in a problem is removed.

This is a good time to re-enforce the importance of checking answers. Pupils should be checking their values work for both pieces of information. They could use a calculator here to help.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

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Starter quiz

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6 Questions

Q1.
Which equation is true for $$x = 4$$ and $$y = 5$$?
$$2x + y = 9$$
Correct answer: $$2x + 3y = 23$$
$$4x + y = 20$$
Q2.
If I add together the pair of simultaneous equations $$9x + 3y = 10$$ and $$6x + y = 30$$, what is the resulting equation?
Correct Answer: 15x + 4y = 40
Q3.
Which equation is true for $$x = 4$$ and $$y = 6$$?
Correct answer: $$3x + 2y = 24$$
$$3x + y = 20$$
$$x + 2y = 14$$
Q4.
If I add together the pair of simultaneous equations $$3x + 2y = 10$$ and $$3y - 3x = 40$$, what is the resulting equation?
Correct Answer: 5y = 50
Q5.
Which equation is true for $$x = -2$$ and $$y = 5$$?
$$3x + 2y = 6$$
Correct answer: $$3x + 2y = 4$$
$$3x + 2y = 11$$
Q6.
If I add together the pair of simultaneous equations $$13x + 2y = 10$$ and $$7x - 2y = 40$$, what is the resulting equation?
Correct Answer: 20x = 50

Exit quiz

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6 Questions

Q1.
If ◉ ◉ ◯ = 25 points and ◉ ◉ ◯ ◯ = 30 points, what is the value of ◉?
Correct Answer: 10, 10 points
Q2.
If ◉ ◉ ◯ ◯ = 18 points and ◉ ◯ ◯ = 11 points, what is the value of ◉?
Correct Answer: 7, 7 points
Q3.
If ◉ ◉ ◯ ◯ = 20 points and ◉ ◯ ◯ = 12 points, what is the value of ◯?
Correct Answer: 2, 2 points
Q4.
If ◉ ◉ ◯ = 23 points and ◉ - (◯) = 10 points, what is the value of ◯?
Correct Answer: 1, 1 point
Q5.
If ◉ ◉ ◯ = 17 points and ◉ - (◯) = 10 points, what is the value of ◯?
Correct Answer: -1, -1 point
Q6.
If ◉ ◉ ◉ ◯ = 33 points and ◉ ◉ ◉ ◯ ◯ = 36 points, what is the value of ◉?
Correct Answer: 10, 10 points