Question

Maria is ordering copy paper for her office. The office is low on white paper and on blue paper. She will pay $3.50 per ream of white paper and $3.75 per ream of blue paper. If the purchase order is for $36.00 and she ordered 10 reams of paper, how many reams of white paper will she receive?

Answer 1

w + b = 10 <--- she ordered 10 reams of paper (both white and blue)
3.5w + 3.75b = 36

Those are the equations we will use and we will solve by substitution.
w + b = 10
b = -w + 10
so we will sub -w + 10 in for b in the other equation.

3.5w + 3.75b = 36
3.5w + 3.75(-w + 10) = 36
3.5w - 3.75w + 37.50 = 36
3.5w - 3.75w = 36 - 37.50
-.25w = -1.50
w = -1.50/-0.25
w = 6

w + b = 10
6 + b = 10
b = 10 - 6
b = 4

check..
3.5w + 3.75b = 36
3.5(6) + 3.75(4) = 36
21 + 15 = 36
36 = 36 (correct)

she will receive 6 rolls of white paper and 4 rolls of blue paper