How much pure alcohol must be added to 100 liters of 10% alcohol solution to create an 80% solution?

Question

How much pure alcohol must be added to 100 liters of 10% alcohol solution to create an 80% solution?

Answer 1

Look at it like this:  there is 100 L of 10% solution and x L of 100% solution; Add them together and you get (100 + x) L of 80% solution.  Now just write it as an equation:

 

.10(100) + 1.00(x) = .80(100 + x)

10 + x = 80 + .8x

.2x + 70

x = 350

 

So the answer is 350 liters of pure alcohol.