Expert: Steve Holleran - 3/16/2008

Question
Sarah, a pharmacist, has a 60% solution of sodium iodine. She also has a 25% solution of the same solution. How much of each solution should she mix to make 6 liters of a 40% solution.

Answer
Hi Brian,

Okay, here's what we've got:

solution:               60%          25%                  40%

amount                   x                                 6

This means we can call the amount of 25% solution 6-x.

Then the amount of sodium iodine in the first two solutions has to equal the amount in the final (40%) solution:

               .60x + .25(6-x) = .40(6)

               .60x + 1.50 - .25x = 2.40

               .35x = 2.40 - 1.50 = 0.90

   so             x = 0.90 / .35 = 2.57

So she should use 2.57 L of the 60% and 3.43 L of the 25%

Hope this helps
Steve