Question

If $8x-9y=20$ and $7x-10y=9$, then what is $2x-y$ equal to?

• A. $10$
• B. $11$
• C. $12$
• D. $13$

Answer 1

The correct option is A $10$

Given:

$8x-9y=20$ ........... $\left(1\right)$

$7x-10y=9$ ......... $\left(2\right)$

Multiplying $\left(1\right)$ by $7$ and $\left(2\right)$ by $8$ and then subtract $\left(2\right)$ from $\left(1\right)$, we get

$(56x-63y)-(56x-80y)=140-72$

$\Rightarrow 17y=68$

$\Rightarrow y=4$

Now, put $y=4$ in (1)

$8x-9\times 4=20$

$⟹8x=20+36=56$

$⟹x=7$

Now $2x-y=2\times 7-4=10$