Question 477899
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Hi,
Solution A is 20% acid ...to new solution 5L that is 18% acid 
Will set question up as to the % of water
Let x represent the amount of pure water 
and (5L-x) represent the amount of 80% water solution (20% acid)
Mixing to form a 82% water solution
x + .80(5-x) = .82*5
    .20x =  .02*5
       x = .02*5/.20
       x = .5L of water