Later, the teaching assistant in Bob's chemistry course gives him some advice. "Based on past experience," the teaching assistant says, "working on 70 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

1 hour working on problems, 3 hours reading

Explanation:

the question is not complete:

Bob is a hard-working college freshman. One Tuesday, he decides to work nonstop until he has answered 200 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       Marginal gain

8:00 AM                         0    

9:00 AM                        80                                        80

10:00 AM                     140                                        60

11:00 AM                      180                                        40

Noon                          200                                        20

Since Bob's is able to answer more than 70 questions per hours only during one hour (from 8 to 9 AM), he can benefit more from reading the next 3 hours. Reading would be equivalent to answering 210 questions, while Bob was only able to answer 120 more questions in the following 3 hours.