Answer:
350 white copies and 50 coloured copies
Step-by-step explanation:
$0.10 per coloured copy (c)
$0.05 per white copy (w)
$22.50 total bill
c = number of coloured copies
w = number of white copies
400 = number of total copies
<em>Write a system of equations:</em>
c + w = 400; c = 400 – w
0.1c + 0.05w = 22.5
<em>Replace one variable in the more complex equation:</em>
0.1(400 – w) + 0.05w = 22.5
<em>Solve:</em>
0.1(400 – w) + 0.05w = 22.5
40 – 0.1w + 0.05w = 22.5
40 – 0.05w = 22.5
–0.05w = 22.5 – 40
–0.05w = –17.5
w = –17.5 ÷ –0.05
<u>w = 350</u>
c = 400 – w
c = 400 – 116.7
<u>c = 50</u>
