Question

Maria is ordering copy paper for her office. The office is low on white paper and on blue paper. She will play 3.50 per ream of white paper and 3.75 per ream blue paper. If she payed $36.00 and bought 10 reams of paper, how many white reams does she have

Answer 1

So we know that the decimal place will move one right. Well basically let's assume she could have bought these expressions:

x 10 x 3.50 = 35.00
x 9 x 3.50 = 31.50 + 3.75 = 35.25
x 8 x 3.5 = 28 + 3.75 x 2 = 35.5
x 7 x 3.5 = 24.5 + 3.75 x 35.75

We know that there is a pattern. See how the cents goes .25 up each time. So we know she'd buy 6 reams of white because (6 x 3.5 = 21) + (4 x 3.75 = 15) = 36.

Answer 2

w + b = 10
3.50w + 3.75b = 36.00

Rewrite the first equation for w then plug it into the second equation.
w = 10 - b
3.5(10 - b) + 3.75b = 36.00
35 - 3.5b + 3.75b = 36.00
35 + .25b = 36
Subtract 35 from both sides.
.25b = 1
Divide both sides by .25
b = 4
w + b = 10
w + 4 = 10
Subtract 4 from both sides
w = 6
White = 6
Blue = 4