Subtract within 20
Lessons in this chapter
About Subtract within 20
Take Apart introduces subtraction as more than removal: it is also how you answer how many more, which is the use kids find hardest and need most.
Perform Subtraction as Taking Away is the version everyone starts with, and it matches what the words describe. Seven cars, three drive away, four left. It is concrete, it can be acted out, and it gives kids a reliable first meaning for the minus sign.
Work with Subtraction Facts up to 5 asks for the small differences to be known rather than recounted, the same way Put Together did for addition. These facts also start linking the two operations together, because a child who knows 2 + 3 is 5 has most of what is needed to see that 5 − 3 is 2.
Use Subtraction to Compare is the lesson that does the real work. Asking how many more apples one child has than another is a subtraction, but nothing is taken away, so kids who only know subtraction as removal get stuck. Meeting the comparison model here, in kindergarten, is what stops it being a problem in later grades.
The three lessons each open as a worksheet in the page. Perform Subtraction as Taking Away and Work with Subtraction Facts up to 5 cover the familiar kind, and Use Subtraction to Compare carries the harder math problems, the how many more ones where nothing is removed at all. All three are free and scored as you go.
Frequently asked questions
Three lessons. Perform Subtraction as Taking Away introduces subtraction as removal, Work with Subtraction Facts up to 5 asks for the small ones by recall, and Use Subtraction to Compare covers the harder case: how many more one group has than another, where nothing is taken away. It sits in Operations and Algebraic Thinking (K.OA) in the Common Core, which keeps kindergarten subtraction within 10.
Two things: taking some away from a group, and comparing two groups to find how many more one has. Take Apart teaches both, and the second is the one kids usually find harder.
Because “how many more” problems are everywhere, and a child who only knows subtraction as taking away does not recognize them as subtraction at all. Meeting the idea now prevents that.
The ones up to 5, so 5 − 2, 4 − 1, 3 − 3 and the rest. Work with Subtraction Facts up to 5 is the lesson for it.
Through the small facts. A child who knows 2 + 3 is 5 can usually see that 5 − 3 is 2. The formal version, fact families, comes in 1st grade, but the connection starts here.
Because nothing is being removed, so it does not look like subtraction. Lining the two groups up side by side and matching them one to one shows the leftover, and that leftover is the answer.