Relate Addition and Subtraction
Lessons in this chapter
About Relate Addition and Subtraction
Addition and Subtraction are Related is a short chapter carrying one large idea: these are not two separate operations but two directions through the same fact.
Work with Fact Families Using Number Bonds introduces the number bond, a picture showing a whole split into two parts. From the parts 3 and 5 and the whole 8 come four facts: 3 + 5 = 8, 5 + 3 = 8, 8 − 3 = 5 and 8 − 5 = 3. Learning them as a family rather than four separate things roughly halves what has to be memorized.
Use Addition to Subtract and Subtraction to Add then makes it a working method. A child stuck on 13 − 8 can ask what adds to 8 to make 13, which is often a fact they already know, and a child who has just added can check it by subtracting back.
This is also where the equals sign starts meaning balance rather than “here comes the answer”. A number bond shows 3 + 5 and 8 as the same amount written two ways, which is the reading kids need before algebra asks them to solve for a missing value.
Both lessons open as worksheets in the page. Work with Fact Families Using Number Bonds and Use Addition to Subtract and Subtraction to Add ask for the same three numbers rearranged, which is the idea of the chapter put into worksheet form. Two lessons, free, scored as you go.
Frequently asked questions
Two lessons. Work with Fact Families Using Number Bonds shows that 3, 5 and 8 make four facts rather than four separate things to learn, and Use Addition to Subtract and Subtraction to Add puts that to work, so a child stuck on 8 minus 5 can ask what adds to 8 instead. It sits in Operations and Algebraic Thinking (1.OA).
A set of four related facts from the same three numbers. From 3, 5 and 8 come 3 + 5 = 8, 5 + 3 = 8, 8 − 3 = 5 and 8 − 5 = 3.
A picture of a whole split into two parts, with the whole in one circle and the parts in two others. It shows at a glance why a fact family works.
By turning the question round. Instead of taking 8 from 13, ask what adds to 8 to make 13. Kids often know the addition fact when the subtraction one feels unfamiliar.
Because it is one idea applied twice: see the family, then use it. It is short, but almost everything in Double Digit Addition and Subtraction depends on it.
A child who learns four separate facts has four things to remember. A child who learns one family of three numbers has one, and can produce all four facts from it.