Carlos is a hard-working college senior. One Saturday, he decides to work nonstop until he has answered 100 practice problems for his physics 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 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 Carlos’s second hour of work, from 9:00 AM to 10:00 AM, isproblems.

The marginal gain from Carlos’s fourth hour of work, from 11:00 AM to noon, isproblems.

Later, the teaching assistant in Carlos’s physics course gives him some advice. "Based on past experience," the teaching assistant says, "working on 25 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?

a. 1 hour working on problems, 3 hours reading
b. 2 hours working on problems, 2 hours reading
c. 3 hours working on problems, 1 hour reading
d. 4 hours working on problems, 0 hours reading