Question

If $5x-10y=20$ and $10x+20y=40$ then find the value of $x$ by using the substitution method.
$\left[2\right]$
[2 Marks]

Answer 1

Solution:
The given equations are,
5x - 10y = 20 ....(1)
10x + 20y = 40 ....(2)
From Eqn. (1) $y=\frac{5x-20}{10}=\frac{x}{2}-2$
[1 Mark]

Putting the value of $y$ in eqn. (2)
$10x+20\times (\frac{x}{2}-2)=40$
$\therefore 10x+10x-40=40$
$\therefore 20x=80$
$\therefore x=\frac{80}{20}=4$
[1 Mark]
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