Achemist has 100g of 25% acid solution. how much of these solution he needs to drain and replace with 70% acid solution to obtain 100g of 60% acid solution?

let us assume x=amt of 25% solution to drain and replace with 70% solution 25%

   25%(100-x)+70%x=60%100

   25-.25x+.70x=60

   .50x=35

   x=70

       so he needs to drain and replace 70 mg of these solution to obtain 100g of 60% acid solution.