A decision at the margin

Frances is a hard-working college senior. One Tuesday, she decides to work nonstop until she has answered 100 practice problems for her physics course. She starts work at 8:00 AM and uses a table to keep track of her progress throughout the day. She notices that as she gets tired, it takes her longer to solve each problem.

Time

Total Problems Answered

8:00 AM09:00 AM4010:00 AM7011:00 AM90Noon100

Use the table to answer the following questions.

The marginal, or additional, gain from Frances's second hour of work, from 9:00 AM to 10:00 AM, is

problems.

The marginal gain from Frances's fourth hour of work, from 11:00 AM to noon, is

problems.

Later, the teaching assistant in Frances's physics course gives her 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 her 4 hours of study time to get the best exam score possible, how many hours should she have spent working on problems, and how many should she have spent reading?

0 hours working on problems, 4 hours 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