Hi,

dilute the 70% alcohol solution into 20% alcohol solution using sterile H2O

  water = water

 x + .30A = .80(A+x)

      .20x = .5A

         x = .5A/.2

         x = 2.5A     Add 2.5 times as much water as the amount of 70% solution used



For ex:  using 10L of 70% solution  ⇒  

   

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