SOLUTION: I need to reduce 1 litre of 40% alcohol to 28% how much water do I need to add? (should have listened better at school I guess!!) Joe

Question 611122: I need to reduce 1 litre of 40% alcohol to 28% how much water do I need to add?
(should have listened better at school I guess!!)
Joe
Answer by vleith(2983) (Show Source): You can put this solution on YOUR website!
You will find many problems that involve "how much of this do I need to mix with how much of that in order to get xx in a total'. This problem is the simplest case of that type of problem. usually you have two solutions with different percentages. In your case, you have two. But one of them is at 0%.
You can do it the hard way (the way one would if what you were mixing had something other than 0).But for this one, let's do it the easy way.
There is some amount of alcohol in the initial sample (in this case it is 0.4 liters worth since you have 1 litre of 40% solution)
How many liters of 28% solution would you need in order to have 0.4 litre of alcohol?

you would need 1.42 liters of a 28% solution.
So now you know how much the total volume is.
You started with 1 liter at 40% and are asked 'how much water to you have to add to dilute that to a 28% solution?"
Answer 1.42-1 = 0.42 liters of pure water.
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