Challenging and different!
Adding and subtracting "Mixed denominate numbers" is a great way to further your students understanding of the most basic operations in math, and, at the same time, to develop their basic concepts of measurement. Denominate numbers build on their skill of carrying and borrowing, but in a new and interesting way.
This product was originally posted at my colleague's store: Room 213.
One foot is twelve inches. When we add and subtract measurements that contain both feet and inches, new challenges arise. Students must recognize that we don't carry over with groups of ten, but with groups of twelve. Similarly, in subtraction, borrowing from the feet column produces twelve inches not ten as they are accustomed to in the conventional algorithm with ones, tens, hundreds columns, etc.
Students will benefit greatly from the additional steps necessary to complete the problem. It will further their understanding of the basic premises behind the methods they've learned previously.