Time	Total Problems Answered
8:00 AM	0
9:00 AM	80
10:00 AM	140
11:00 AM	180
Noon	200

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, is

problems.

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

problems.

Later, the teaching assistant in Carlos's chemistry course gives him some advice. "Based on past experience," the teaching assistant says, "working on 30 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