Mathematics

The boys mixed 10 gallons of the 20% pure lemon juice mix and 10 gallons of the 70% pure lemon juice mix, because they wanted 20 gallons

of lemonade at a 40% lemon juice mixture. They thought that because 40% was almost halfway between 20% and 70%, they should just mix equal

parts of both, but the lemonade turned out too tart. How much of each should they have used to get a final mixture of 20 gallons at 40%

lemon juice? Write your answer in complete sentences. Show all work.