A decision at the margin Bob is a hard-working college freshman. One Tuesday, he decides to work nonstop until he has answered 150 practice problems for his economics course. He starts work at 8:00 AM and uses a table to keep track of his progress throughout the day. He notices that as he gets tired, it takes him longer to solve each problem. Time Total Problems Answered 8:00 AM 0 9:00 AM 60 10:00 AM 105 11:00 AM 135 Noon 150 The marginal, or additional, gain from Bob’s second hour of work, from 9:00 AM to 10:00 AM, is problems. The marginal gain from Bob’s fourth hour of work, from 11:00 AM to noon, is problems. Later, the teaching assistant in Bob’s economics course gives him some advice. “Based on past experience,” the teaching assistant says, “working on 22.5 problems raises a student’s exam score by about the same amount as reading the textbook for 1 hour.” For simplicity, assume students always cover the same number of pages during each hour they spend reading. Given this information, in order to use his 4 hours of study time to get the best exam score possible, how many hours should he have spent working on problems, and how many should he have spent reading? 0 hours working on problems, 4 hours reading 2 hours working on problems, 2 hours reading 3 hours working on problems, 1 hour reading 4 hours working on problems, 0 hours reading