Hi,

how many gallons of a 60% solution must be mixed with 15 gallons of 10% solution 

to obtain a 20% solution?

  .60x + .10*15 = .20(15+x) ***   |Multiplying thru by 100

   60x + 150 = 20(15+x)    |Solve for x

      40x = 150

        x = 15/4gallons  0r  33⁄4 gal

 CHECKING our answer***

   2.25 + 1.5 = 3.75  

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