SOLUTION: I have 200 liters of 89% alcohol. I need to dilute it to 43%. How much water will I need?

We’re diluting, so we need to DRAIN a certain amount from the solution, then add that same amount of WATER that was drained



Let amount of solution to be drained, or amount of water to be added back, be W

Amount of water in solution: 11%, or .11 (1 - .89), and amount of water in diluted solution: 57% or .57 (1 - .43)

Thus, we have the following WATER equation: Water + water = water, OR

.11(200 – W) + W = .57(200)

22 - .11W + W = 114

.89A = 114 – 22

.89A = 92

W, or amount of solution to drained (amount of water to add) = , or 



By the way, when you drain 103.3708 L from the solution, and add back 103.3708 L of water, you'll be left with 114 L of water, and 86 L of

alcohol, which is 57% water and 43% alcohol.



Remember that the 200 L of liquid that you start off with DOES NOT change. The only things that change are the amounts of alcohol and 

water in the desired solution. You start off with 178 L of alcohol and 22 L of water, and end up with 86 L of alcohol and 114 L of water



If however, you're not draining and adding back what you drained, then the amount of water you need is is 213.95 L