Question

A medicine for the relief of asthma can be purchased from 5 different manufacturers in liquid, tablet, or capsule form, all of which come in regular and extra strength. How many different ways can a doctor prescribe the drug for a patient suffering from asthma? 

Answer 1

Since the event "manufacturer of medicine" , the event "form of medicine" and the event "strength of medicine" are independent events, then a doctor can prescribe the drug for a patient suffering from asthma in $5\cdot3\cdot2=30$ different ways.