Question 729631
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How many liters each of 8%, 10%, and 20% hydrogen peroxide should be mixed together to get 8 liters 
of 12.5% solution, if the amount of 8% solution used must be 2 liters more than the amount of 20% solution used?
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Ingredients: x liters of the 20% hydrogen peroxide;

             (x+2) liters of the 8% hydrogen peroxide;

              and (8 - x - (x+2)) = 6-2x liters of the 10% hydrogen peroxide.


Write equation for the content of hydrogen peroxide

    0.2*x + 0.08*(x+2) + 0.1*(6-2x) = 0.125*8.


Simplify and find x

    0.2x + 0.08x + 0.16 + 0.6 - 0.2x = 1,

    0.2x + 0.08x - 0.2x = 1 - 0.16 - 0.6

           0.08x        =     0.24

               x        = 0.24/0.08 = 3.


<U>ANSWER</U>.  Use 3 liters of the 20% hydrogen solution PLUS 3+2 = 5 liters of the 8% hydrogen solution 

         and do not use the 10% hydrogen solution, at all.


<U>CHECK</U>.  The final concentration will be  (0.2*3 + 0.08*5)/8 = 1/8 = 0.125 = 12.5%,   correct.
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Solved.