Question 35083
Here's the problem: Susan Staples, a pharmacist, has a 60% solution of the drug sodium iodite. She also has a 25% solution of the same drug. She gets a prescription calling for a 40% solution of the drug. How much of each solutionshould she mix to make 0.5 liter of the 40% solution?

Let amount of 60% solution be "x" liters 
Then amount of 25% solution must be "0.5-x" liters
Amount of sodium iodite in the 60% batch is 0.60x liters
Amount of sodium iodite in the 25% batch is 0.25(0.5-x)=0.125-0.25x liters
EQUATION:
 sodium iodite + sodium iodite = 0.40(0.5 liters)
 0.60x + 0.125-0.25x = 0.20 liters
 Multiply thru by 1000 to get:
600x +125 - 250x = 200
350x=75
x=0.214 liters (amount of 60% solution)
0.5-x= 0.5-0.214= 0.286 liters  (amount of 25% solution)
Cheers,
stan H.