Question 1174695
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Hi
A 40 liter of 30% ethyl alcohol: How much  "x"  of a 20% ethyl alcohol should be added to reduce the concentration to 25% ethyl alcohol. 
  .30(40L) + .20x = .25(40+x)
         .05(40L) = .05x
             x = 40L of a 20% ethyl alcohol should be added
  12 + 8 = (1/4)80  checks
         
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