Question

If 3 computer disks and 5 notebooks cost $7.50 and 4 computer disks and 2 notebooks cost $6.50, how much does 1 computer disk cost?Group of answer choices$0.75

Answer 1

let x be the price of the computer disc and let y be the price of the notebooks.

Given the information on the problem, we can write the following equations:

$\begin{gathered} 3x+5y=7.50 \\ 4x+2y=6.50 \end{gathered}$

we can solve for y on the second equation to get the following:

$\begin{gathered} 4x+2y=6.50 \\ \Rightarrow2y=6.50-4x \\ \Rightarrow y=\frac{6.50}{2}-\frac{4x}{2}=3.25-2x \\ y=3.25-2x \end{gathered}$

then, we can substitute this expression on the first equation to get the following:

$\begin{gathered} 3x+5(3.25-2x)=7.50 \\ \Rightarrow3x+16.25-10x=7.50 \\ \Rightarrow-7x=7.50-16.25=-8.75 \\ \Rightarrow x=\frac{-8.75}{-7}=1.25 \\ x=1.25 \end{gathered}$

therefore, the cost of 1 computer disk is $1.25