Question

A housepainter buys 40 gallon-size cans of paint for $920. Some of these are blue paint that cost $30 per gallon and the rest are white paint that cost $20 per gallon. How many gallons of white paint does the painter buy?

Answer 1

28

Explanation:

x=blue

y=white

x+y=40

30x+20y=920

30(x+y=40) ; 30x+30y=1200___[1]

30x+20y=920 ; 30x+20y=920___[2]

[1]-[2] : 30x+30y-30x-20y=1200-920

10y=280

y=28

painter buys 28 white gallons