Question 426625
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Hi
Let x represent the amount of pure salt(100%) added...
  Mixing to form (24kg+x)of 40% solution
   .20*24kg + x = .40(24kg+x)
           .60x = .20*24kg
              x = .20*24kg/.60
              x = 8kg, the amount of pure salt that needs to be added

CHECKING our Answer***
   4.8kg + 8kg = 12.8kg = .4*32kg = 12.8kg