It is a bit nasty but the same skills are often being tested and not printing every solution might save the business big dollars on printing etc..
Why is it that there are so many math books which only give answers only to the odd-numbered or only to to the even-numbered problems in the book, and then you have to buy a 'solution manual' to get the rest of the answers? If I do choose to solve the even numbered problems I have to go through a process (sometimes quick, sometimes long) of checking my answer that takes time, and in today's college world time is of the essence. Anyone feel that it is just downright mean?
This is an even "meaner" way to look at it: You need to build confidence by doing work that you haven't been given a final answer to. The so-called real life doesn't provided a source with the final answer worked out.
It sounds awful, but I taught HS for 2 years and I've done several at different colleges. What I have found is an alarming number of students insisting I give them problems that come out to "easy" answers, such as g = 10 versus g = 9.81 because if they get the g = 10 they know they've got it right. I'm evil: The only problem I gave that had an "easy" answer to was one that came out to 1.21 Gigawatts (from "Back to the Future.") and they didn't even get the reference.
@topsquark The ones who are evil are those that are giving the answers that come out as g=10... they're not training the kids to face the kinds of numbers in real science that they would see most of the time...
So with algebra and differential calculus a lot of answers get shown simply by entering the equations in a graphing program or calculator. But then it starts getting nasty when we get to integral calculus where you have no choice but to differentiate in order to see if it matches what you integrated (you can still use a calculator to show it), and even worse in differential equations... you can only graph one particular solution at a time, but the only way to check is to get the derivative/s of y and see if it satisfies the DE, I havent yet seen a calculator function for this.. It seems the only way to check a DE is to use special software, such as MAPLE, etc..
I always figured that text books don't give answers to all problems so that the instructor has the option of assigning homework problems where the answer is not given. That way he can seee if the students understand what they are doing, and if they have the skills to check their own work.