Question

what amout of 1% milk and what amount of 4% milk would you mix to make 5 gallons of 2% milk?

Answer 1

5 gallons of 2% milk = 0.10 gallons of milk
1 gallon of 1% milk = 0.01 gallons of milk
1 gallon of 4% milk = 0.04 gallons

x + y = 5
0.01x + 0.04 y = 0.10
so that simplifies to
x + 4y = 10
x + y = 5
So 3y = 5
y = 5/3 or 1.6667 gallons
x = 10/3 or 3.333 gallons