Subtraction Basic Facts - Think Addition Strategy . Subtraction basic facts are the set of subtractions that relate to the addition basic facts. The largest total for subtraction basic facts is 18 as this is the total for the addition basic fact 9 9. . The aim for learning basic facts is for them to be known automatically. Students can use work done and their knowledge of addition basic facts to help recall subtraction basic facts. . The strategies for addition can assist students to recognise t