Question 1034619
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 Hi, the pharmacist gives me a 1.5 liter bottle of 20% solution and asks me to mix with water to make as much 12% solution as possible. 
How much water will I use?
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<pre>
Let x be the volume of water to add, in liters.

Then the volume of the new solution is 1.5 + x liters.
The original 1.5 liters of solution contains 1.5*0.2 liters of the pure substrate (remember, 0.2 = 20%).

So, you have this equation to find x:

{{{(1.5*0.2)/(1.5 + x)}}} = 0.12,

where 0.12 is the concentration of the new solution.

To solve it, multiply both sides by (1.5+x), and you will get

0.3x = 1.5*0.12 + 0.12x,

0.3x - 0.12x = 0.18,

0.18x = 0.18,

x = 1.

<U>Answer</U>.  1 liter of water should be added.
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