Year 9

# Eliminating a variable

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## Lesson details

### Key learning points

- In this lesson, we will determine how to eliminate a variable by adding or subtracting one equation to or from the other.

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### 5 Questions

Q1.

If x=3 and 2x+5y=41, what is the value of y?

3

5

7.8

Q2.

7x+2y=24 AND 4x+2y=18. Find the value of 3x

2

5

7

Q3.

7x+2y=24 AND 4x + 2y = 18. Find the value of y

2

6

7

Q4.

9x +6y=168 AND 9x +4y=160. Solve

Others

x=15 and y = 18

x=9 and y=6

y=16 and x=4

Q5.

4x +8y=116 AND 4x +4y=68. Solve

x=12 and y=5

x=4 and y = 8

x=8 and y = 4

### 5 Questions

Q1.

3x+2y=5 AND 3x-2y=7. If I add these two equations together, which unknown will be eliminated?

both

neither

x

Q2.

3x+2y=5 AND 3x-2y=7. If I subtract the two equations, which unknown will be eliminated?

both

neither

y

Q3.

3x-5y=17 AND 2x-5y=10. Subtract the first equation from the second equation.

5x=27

x-10y=7

y=7

Q4.

2x-5y=10 AND 3x-5y=17. Add the two equations together.

10y=27

5x=27

Q5.

3x-5y=17 AND 7x-5y=20. How can I eliminate y from these simultaneous equations?

add

you can't eliminate y