# Addition and Subtraction within 20

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.

## Prior Learnings

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).

## Future Learnings

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:

1. Use objects and drawings to illustrate word problems with situations like adding, removing, combining, taking apart, or comparison.
2. Write equations involving adding, removing, combining, taking apart, or comparison situations involving unknown numbers that change positions.
3. Explain how an equation represents one of the above situations.
4. Solve word problems that represent one of the above situations.

## 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

**[Addition Subtraction under 20 - 1st Grade Math Videos for Kids](https://www.youtube.com/watch?v=FDP0mbsVX9A)**  
Math & Learning Videos 4 Kids

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.

1. **Word Problem 1:** “Sam has 4 hats and Josh has 8 hats. How many hats do they have altogether?”  
   - The video shows how many hats each has. Your students can draw their own hats on a piece of paper.  
   - The total is counted, starting from 8 and adding 4, resulting in 12 hats.

2. **Word Problem 2:** “Henry has 4 fewer cats than John. John has 9 cats. How many cats does Henry have?”  
   - Understanding “fewer” indicates subtraction.  
   - Henry ends up with 5 cats after the subtraction.

3. **Word Problem 3:** “Sam has 3 more pumpkins than Jim. Jim has 6 pumpkins. How many pumpkins does Sam have?”  
   - Starting with Jim’s known amount, Sam’s total is calculated as 9 pumpkins.

4. **Word Problem 4:** “Cindy has 7 cakes. Suzy has 9. How many more cakes does Suzy have than Cindy?”  
   - Subtraction reveals Suzy has 2 more cakes than Cindy.

### Video 2: Adding and Subtracting Flowers and Balloons

**[Addition and Subtraction within 20 - 1st Grade Math (1.OA.1)](https://www.youtube.com/watch?v=zJyT6MIlkAw)**  
Boddle Learning

In this video, Boddle starts with 5 yellow flowers and engages students in counting how many flowers Peter has in total after he finds more.

1. Boddle counts the flowers and totals to 7.
   - Another problem asked is “What is 8 + 4?”, with the total being 12.

2. The video covers subtraction: “There are 6 friends playing. Two go home early.”  
   - This results in 4 remaining friends.
   - Another subtraction problem is 10 - 3, concluding with 7 remaining balloons.

## Want more practice?

Give your students additional standards-aligned practice with Boddle Learning. Boddle includes questions related to Comparing and Measuring Lengths plus rewarding coins and games for your students to keep them engaged.