Understanding addition and subtraction within 20 is a first grade, Common Core math skill: 1.OA.1. Below we show two videos that demonstrate this standard. Then, we provide a breakdown of the specific steps in the videos to help you teach your class.
Your students should be familiar with the Kindergarten skill of understanding the number partners that equal 10 and knowing all decompositions (e.g. 5=4+1, 5=2+3) of numbers below 10. This skill builds a foundation for strategy development and understanding of place values and properties of operations (K.OA.3-4). Your students should also understand that ten 1’s plus more 1’s are considered “teens” (K.NBT.1).
Understanding how to perform addition and subtraction within 20 will enable your students to perform similar skills up to 100, eventually extending those skills to work with larger numbers and solve two-step word problems (2.OA.1). They will also be able to apply this skill with problems in a variety of contexts involving length, picture graphs and bar graphs (2.NBT.5).
Common Core Standard: 1.OA.1 - Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions.
Students who understand this principle can:
2 Videos to Help You Teach Common Core Standard: 1.OA.1
Below we provide and breakdown two videos to help you teach your students this standard.
Video 1: Adding and Subtracting with Mr. Robot
The video presents four word problems with addition and subtraction problems for your students to follow along with. Mr. Robot helps the teacher in the video clear the board and engages with the students.
The first word problem states that “Sam has 4 hats and Josh has 8 hats. How many hats do they have altogether?”
The second word problem states that “Henry has 4 fewer cats than John. John has 9 cats. How many cats does Henry have?”
The third word problem states that “Sam has 3 more pumpkins than Jim. Jim has 6 pumpkins. How many pumpkins does Sam have?”
The fourth word problem states that “Cindy has 7 cakes. Suzy has 9. How many more cakes does Suzy have than Cindy?”
Video 2: Adding and Subtracting Flowers and Balloons
In the video, Boddle starts with 5 yellow flowers. She then gives them to her friend, Peter. As Peter walks in the park, he finds 2 more flowers. Boddle asks your students how many flowers Peter has in total now.
The video gives another addition problem for your students to solve, asking “What is 8 + 4?”
The second part of the video covers subtraction. There are 6 friends playing at the park. Two of them have to go home early. How many of them are left?
The second subtraction problem is 10 - 3.
Want more practice?
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*Information on standards is gathered from The New Mexico Public Education Department's New Mexico Instructional Scope for Mathematics and the Common Core website.