theophylline, an asthma medicine, is to be prepared from an elixir with a drug concentration of 5mg/mL and a cherry-flavored syrup that is to be added to hide the taste of the drug. how much of each must be used to prepare 100 milliliters of solution with a drug concentration of 2mg/mL
If x mL of the elixir are used, then the rest (100-x) is syrup. So, using the amount of drug present,
5x + 0(100-x) = 2*100
x = 40
makes sense, since 2/5 = 40/100