Question

Solve for $x$ and $y$:
$0.4x+0.3y=1.7$,
$0.7x-0.2y=0.8$.

Answer 1

$0.4x+0.3y=1.7...\left(1\right)$,
$0.7x-0.2y=0.8....\left(2\right)$.

Multiply both the equations by $10$, we get
$4x+3y=17...\left(1\right)$
$7x-2y=8...\left(2\right)$

Multiply $\left(1\right)$ by $2$ and $\left(2\right)$ by $3$,
$8x+6y=34$
$21x-6y=24$
Adding both the equations
$29x=58$
$x=2$

From $\left(1\right):4\times 2+3y=17$
$\Rightarrow 8+3y=17$
$\Rightarrow 3y=17-8=9$
$y=3$

Answer : $x=2,y=3$