## Adding and Subtracting Within 20

#### Aligned To Common Core Standard:

**Grade 1 Operations** - OA.6

Tips for Adding and Subtracting Within 20 -
Addition and subtraction are something you will see yourself doing every now then, be it counting your pocket money, or counting students in your class. 'Putting together' of two things or objects, and counting how many in all are known as Addition, while subtraction tells you 'how many are left' or 'how many are less in all'. Learning to solve quick addition and subtraction sums or doing mental mathematics will save you time and make you the star of the class.
To be the star of the class, learn addition and subtraction within 20 by following these steps:
**1) Memorize the numbers** - Start with 1 and count till 10. Say out loud and learn it by heart. Do this regularly to get a grasp on numbers from 1 to 20.
**2) Use small objects to add or subtract** - Use objects to add or subtract numbers from 1 to 20. Lay them on a table and start playing. Objects like Legos, popsicle sticks, and wooden blocks are helpful to add and subtract quickly.
**3) Use flashcards with numbers** - Use UNO cards with numbers written on them or make your own flashcards. To learn addition, add more cards to the existing one and find the answer, to subtract, select a number and take away cards, and you have the answer.
These worksheets focus on really small forms of addition and subtraction. They will really help students at this level.

- Sums and Differences Under 20 : Step-by-step Lesson- Use sums and differences in short word based format.
- Add or Subtract Pictures Practice 5 Pack- Visuals really help this one sink in well.

- 9 Problem Set Guided Lesson - Use the sentence based work and convert it to functional numbers.
- Detailed Guided Lesson Explanation - I really work through each step for you in high detail to insure you understand it.

- Word Problem Form Practice Worksheet - All addition and subtraction takes place in the form of word problems. There is plenty of space to work it out.
- Matching Problems to Answers Worksheet - This is a little bit more advanced. You add and subtract 2 sets or 3 sets of digits.
- Guided Lesson 1 - We ask you to think deep and that teachers accept endless possible answers. We are working with values that are within 0 to 20.
- Guided Lesson 2 - You show use the various ways you can use to create an end sum or difference based on the scenario set for you. The values on this worksheet stay within 20.
- Step-by-step Lesson - Look at the number of pencils in the problem below and write the addition equation below it. Name the equation that is at work with this set.
- Subtraction within 20 Lesson 2 - Flower it up with the correct difference. There are 8 flowers first group from left. 3 clocks are in the second group which are crossed out. We subtracted 3 from 8 and then counted the flowers that are left there.
- Addition within 20- Time to break the boxes back out. Find the sum of the number of cubes given in the equations.
- Box Operations Practice- Remind students that both addition and subtraction are going on here.
- Matching Worksheet - Time to match up the differences. You will use visuals to represent the integers that are at play here.
- Within 20 Quick Explanation- This can also be seen as a quiz. Add 2 numbers to make 15. Choose a number smaller than 15 and go from there. We chose 10.
- Solving Visual Problems Worksheet - The boxes replace integers and then you process the addtion or subtraction problems that go up to a max value of 20.

#### Guided Lessons

The prompts used here could come from a variety of means.

#### Practice Worksheets

These will include all forms of data because you see that on National exams.

### Example of This Skill:

Problem- **Make the number 8 by: A) adding 3 numbers B) subtracting 2 numbers C) adding 2 numbers.**

The first thing we need to realize is that there are many ways to answer these problems. Which tells us to know that there are many possible solutions. When you are asked a problem that involves addition, you just need to realize that the numbers need to be much smaller than the numbers that the sum needs to be. When you are asked to subtract numbers, you just need to understand that the values must start out much higher that the end value.

**Solutions:** Our final answer for all of these problems must be 8.

a) We are asked to add 3 values together, so the setup really is: __ + __ +__ = 8.

We can choose any value that is at least 2 less than 8. I will choose 3. Now the setup looks like: 3 + __ +__ = 8.

We still need to get to 8. How about we choose the value 1. Now the setup looks like: 3 + 1 +__ = 8.

We just need to determine the value that would make that math sentence true. 3 + 1 + 4 = 8.

b) We are asked to subtract 2 values to result in a final difference of 8. This would look like this __ - __ -__ = 8.

We would need to start with a value much larger than 8, I will choose 18. This would look like this 18 - __ -__ = 8.

We choose a value to subtract from 18, but it cannot result in difference equal to or less than 8. I will choose 6. This would look like this 18 - 6 -__ = 8.

The first difference leaves us with a value of 12. To get the final difference to equal 8, we must subtract 4 from it. In the end we are left with the equation: 18 - 6 - 4 = 8.

c) We are asked to add 2 values together, so the setup really is: __ +__ = 8.

We can choose any value that is less than 8. In fact, we could even choose 8, if we want to. I will choose the number 6. This would leave us with 6 +__ = 8. We then just have to determine what value, when added to 6, equals 8. That value is 2. 6 + 2 = 8.