Đáp án:
The cost of pens, pencils, rulers respectively is: 3$; 2$ and 1,5$
Giải thích các bước giải:
Call cost of a pen is: `x($)`
cost of a pencil is: `y($)`
cost of a ruler is: `z($)`
`(x,y>0)`
We have the equation:
$\begin{cases} 4x+3y=18(1)\\3y+4z=12(2)\\3x+3z=13,5(3) \end{cases}$
From (3) `=> x={13,5-3z}/3=4,5-z`
Replace `x` in `(1)` `=> 18-4z+3y=18 => 3y-4z=0 (4)`
Solve (2) and (4) `=>` $\left \{ {{3y+4z=12} \atop {3y-4z=0}} \right.$
`=>`$\left \{ {{y=2} \atop {z=1,5}} \right.$
`=> x=4,5-z=4,5-1,5=3`
Therefore, the cost of pens, pencils, rulers respectively is: 3$; 2$ and 1,5$