Question

Celano printing recently charged $.49 per page for color copies and nine cents per page for black-and-white copies. If Michaela’s bill for 90 copies was $12.90 how many copies of each type were made?

Answer 1

12 color copies and 78 black-and-white copies.

Explanation:

Let `x=`number of color copies and `y=`number of black-and-white copies. Now set up a system of equations.

`0.49x+0.09y=12.90` `rarr`equation 1
`x+y=90` `rarr`equation 2

Now, solve. I used substitution below.
equation 2
`x=90-y` `rarr`plug into equation 1
equation 1
`0.49(90-y)+0.09y=12.90` `rarr`distribute
`44.10-0.49y+0.09y=12.90` `rarr`isolate y terms
`-0.40y=-31.20` `rarr`completely isolate y
`y=78` `rarr`plug into equation 2
equation 2
`x=90-78`
`x=12`

So, there were 12 color copies and 78 black-and-white copies.