This video demonstrates two subtraction problem structures that students must understand to master basic facts. Each problem structure has three numbers, with one number missing. Take away number problems are a type of change problem when the start quantity is the whole or total amount and the change is the amount taken away to determine the result. Take away number problems are also referred to as separate problems. Compare number problems involve the comparison of two quantities to determine the difference. Although this video illustrates that the result is unknown in both problem structures, students may also use manipulatives to practice basic subtraction facts when a change or a differences is also unknown. A solid conceptual understanding of problem structure results in the ability to transfer knowledge of basic facts to other skills such as word problem solving and computation fluency.