Posted by kate on .
a drug is supplied as a 20 mg/ml solution in a 50 ml vial. you need to make 15 ml of a 10 mg/ml solution. how much concentrate and how much diluent are needed to obtain the desired final volume?

math 
Steve,
you need x ml of solution, and 15x ml of water (0 mg/ml), so
20x + 0 = 10*15
x = 7.5
Since the concentration is being reduced by a factor of 2, the volume needs to be increased by that factor.
2 * 7.5 = 15