I'm always looking for ways to lighten the load of marking. For addition/subtraction, I have my students check their arithmetic by also doing the reverse operation. For example, 28 + 59 = 87, 87 - 59 = 28. This technique can easily be used for multiplication/division as well. It helps them remember that operations are the inverse of each other, and the work is already checked when I receive it. It also ensures that they get an equal workout with the different operations.