In order to get a certain shade of blue paint a mixer must have 5 parts white paint to 3 parts blue. If 4 gallons of paint must be mixed how many gallons of white paint must be used?

3.4 quarts of white.

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If you have 8.5 quarts of blue paint, and you want to use it all in this mixture, then you know that 8.5 quarts is the five parts of blue in this formula.

8.5 quarts divided by 5 equals 1.7 quarts. so 1.7 quarts is your base unit, or 'one part'.

1.7 quarts * 5 = 8.5 quarts (blue)

1.7 quarts * 2 = 3.4 quarts ( white )