4. A decision at the margin Edison is a hard-working college junior. One Saturday, he decides to work nonstop until he has answered 100 practice problems for his chemistry 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 9:00 AM 40 10:00 AM 70 11:00 AM 90 Noon 100 Use the table to answer the following questions. The marginal, or additional, gain from Edison's second hour of work, from 9:00 AM to 10:00 AM, is problems. The marginal gain from Edison's fourth hour of work, from 11:00 AM to noon, is |problems. Later, the teaching assistant in Edison's chemistry course gives him some advice. "Based on past experience," the teaching assistant says, "working on 35 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? 1 hour working on problems, 3 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