Math Teachers: Why do you want students to "show their work?"?

Because it is the basics, the foundation for all higher math formulas and theories. Just because you can do an easy problem in your head doesn't mean you can perform higher functions. If you make a mistake in your head, you will not see it. If it is written down, you or someone else can correct the error. Would you want to pay someone half a million dollars to do a project for you only to hear "Wow, sorry dude, I must have made a mistake in my calculations but I don't know where I went wrong". How would you feel if your parents home was being taken by the bank because someone miscalculated the software program that the bank uses. If your working on a team project, how do you expect the rest of the team to combine their work with yours so everyone gets an A (or only the lazy guy who didn't do his stuff the right was fails and not everybody with him). So for the little time it takes you, always show your work. It's a good habit that will stick with you for the rest of your life. Besides, it took you longer to whine, complain and type out this question than it did to show your work. LOL