SOLUTION: How many milliliters of pure water should a pharmacist add to 40 milliliters of a 5% salt solution to produce a 2% salt solution?

40 milliliters of the 5% salt solution contain  40*0.05 = 2 grams of dissolved salt.


You want to dilute it to 2% concentration by adding pure water.


Let new volume after adding pure water be W milliliters.


You want the concentration   =   be equal to 2%, i.e. 0.02:


     = 0.02.


It implies  W =  = 100 milliliters.


So, the new volume should be 100 milliliters.


It means that you must add  100-40 = 60 milliliters of pure water to get your goal.     ANSWER