# Odd or Even-Numbered Answers in Textbooks

Why do some math (and science) textbooks/solution books only include answers to odd- or even-numbered problems?

Some textbooks have a separately purchased answer book with the missing answers, while others only include odd or even-numbered answers in the solutions book (and none in the textbook). Why is this the case and how do publishers decide this stuff?

• A better question is why aren't the answers given where the problem is stated? Don't we all hate the flipping back and forth? Indeed, this is one of the joys of Churchill's complex variables text. Answers with problems can be very nice. Unfortunately, students misuse answers. – James S. Cook Nov 27 '17 at 2:45
• @DaveLRenfro The question was asked, so presumably it is not obvious. – Tommi Nov 27 '17 at 7:28
• I think it is a commercial thing with instructors finding it better for them but students finding it worse (harder to practice). Very few teachers grade th number of drill problems needed for fluency. And if they do, the feedback lags. Also it makes it harder for people to self study, which again is a commercial thing that empowers paid instructors. [This is not a popular view with paid instructors but should be considered. Economics drives things--just look at editions creep for another example.] – guest Jan 18 '18 at 1:21

1. For very elementary topics in which not much work needs to be shown by students (such as what is the domain of $f(x) = \frac{x}{x^2 – 4}),$ allowing students to have the answers makes it more difficult to grade homework. For example, suppose a student has the correct answer and the student work is not clear, but the work might be on the right track. How much partial credit do you give? If the students are not given the answers, then you can lower your "show your work" bar in deciding on how much credit to give.