Consider the question. Mr. Johnson has a prescription with enough pills for 30 days. After four-fifths of the days, he has 12 pills left. How many pills is Mr. Johnson supposed to take a day if he takes the same dose daily?
 What is the step-by-step reasoning process to arrive at the answer: 2?
Mr. Johnson has been taking the pills for 30 * 4 / 5 = 24 days. He has 30 - 24 = 6 days left to finish the pills. Thus, Mr. Johnson is supposed to take 12 / 6 = 2 pills a day.