Lawrence Hall of Science
The Math Page: Skill in Arithmetic: Add Whole Numbers, Add Decimals
This website explains and defines adding whole numbers and decimals. Content explores addition with regrouping and how to align numbers in a written calculation. There are even practice problems at the end of the lesson.
Lawrence Hall of Science
The Math Page: Skill in Arithmetic: Subtracting Whole Numbers and Decimals
If you are looking for a website that explains and defines subtraction with decimals you have arrived at an excellent resource. There are even practice problems at the very end of the lesson.