CKMath Unit 3: Adding and Subtracting Within 20
Focus:
In this unit, students develop an understanding of 10 ones as a unit called “a ten” and use the structure of 10 + n to add and subtract within 20. Students decompose and recompose addends to find the sum of two or three numbers. For example, to find the value of 9 + 6, they may decompose 6 into 1 and 5, compose the 1 and 9 into 10, and find 10 + 5. Subtraction work occurs throughout the unit and becomes the focus in the last section. Students consider taking away and counting on as methods for subtracting. They understand subtraction as an unknown-addend problem and use their knowledge of addition to find the difference of two numbers. Students solve story problems throughout the unit and learn two new problem types—Add To, Start Unknown and Take From, Change Unknown. Students compare the structure of different types of story problems as they practice adding and subtracting within 20.
Number of Lessons: 27 and 1 optional
Instruction Time:
Approximately 60 minutes
(Please note that each lesson is designed for one instructional block, and may be divided into shorter or longer segments based on teacher pacing and student needs.)
Additional Search Terms:
decompose • recompose • Add To, Start Unknown • Take From, Change Unknown • sum • value
