Answers:
- 1 liter of acid
- 4 liters of water
You got the first question correct, but the second one is wrong. The two values must add up to 5.
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Explanation:
We're told that 20% of this solution is acid. We have 5 liters total, so
20% of 5 = 0.20*5 = 1
Meaning there's 1 liter of pure acid in this solution.
The remaining 5-1 = 4 liters of the solution is water
Or you could note that if 20% is pure acid, then the remaining 80% is water
80% of 5 = 0.80*5 = 4
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Another approach is to realize that 20% is the same as the fraction 1/5
So if 1/5 of the mix is pure acid, and we have 5 liters of the solution, then we must have 1 liter of pure acid
(1 liter of pure acid)/(5 liters of solution) = 1/5 = 20% acid solution
, or 
. Plugging in our value 9 for 
, we get 
.
