## Unknown Numbers in Addition And Subtraction

#### Aligned To Common Core Standard:

**Grade 1 Measurement** - OA.8

This is going to be the first time that students will be confronted with algebraic thinking. This can be very overwhelming for them, or they could embrace it. The best way to approach this new subject matter with them is to present it as a mystery. I usually call this my Math Detective unit. I tell students that now that we have a good on the basic math operations (addition and subtraction), we can now check the work of others. I tend to start this process visually as you will see in the progression of the worksheets. Using word problems that can easily be drawn is a good place to start. Once they get the basic concept of finding missing addends or subtrahends, you are ready to jump into working with actual equations. These worksheets will have students complete problems that undergo an addition or subtraction operation. This is an algebra primer for students. Again, this is most likely the first time that they have seen problems like this and it will require some patience on the part of the teacher. This is not a unit that you will fly through and it will need extra time set aside for it. We encourage you to give them as much practice as is possible within your time frame.

- Banana Thief Step-by-step Lesson-
You have got to hate it when a monkey steals your bananas.

- Visuals To Answer Problems Guided
Lesson - You work through 3 problems that all are basic word
problems with the assistance of the pictures.

- Explanation For Above - We
help you work through all the problems with cross outs and counting
strips.

- Who Done It? - These problems
have you look for answers to intermediate parts of the question.

- Matching Problems To Answers
- Find the answer that matches each question.

#### Guided Lessons

I received many positive comments on this section. I hope you find it useful.

- Guided Lesson Explanation 1 - This shouldn't move at a snail's pace.
- Guided Lesson Explanation 2 - Sea horses again! For real?
- Guided Lesson Explanation 3 - The great sandwich caper.
- Guided Lesson Explanation 4 - The cookie cross out.
- Step-by-step Lesson - Roy and his crazy ice cream bars.

#### Practice Worksheets

I created this section as a primer section for word problems.

- Independent Worksheet- Double digit numbers make an appearance here.
- Match Equations Worksheet- Visual to integer correlations are tough for some kids.
- Matching Worksheet- This might be very difficult for students who haven't worked with higher levels of numbers.
- Practice Worksheet - See if the mice help you solve this one.

### How to Find Unknown Numbers in Addition and Subtraction Equations

### Solving Unknowns in Addition Equations

**Example Problem: Find the unknown value in the equation: 5 + __ = 8**

**Math Based Solution**

**Step 1)** A good way to approach this is to rewrite the problem in what we call mountain format. In this format we write the sum or difference at the top and the parts that create it at the bottom. In this case, 8 at the top and 5 and the unknown (noted by the blank square) at the bottom.

**Step 2)** Since the unknown is being added to 5. We can count up from 5 until we hit our sum. In this case, it requires us to count 3 times.

**Step 3)**This tells us our missing addend is 3.

### Solving Unknowns in Addition Equations

**Example Problem: Find the unknown value in the equation: 5 + __ = 8**

**Model Based Solution**

**Step 1)**You can also model this problem with the use of simple shapes. In this case, I will use a circle. We know the sum is 8. As a result, we will draw 8 circles.

**Step 2)** The sum indicates that you already have 5. We will model this by separating the first five circles. We then just need to count how many circles remain to make the total (8). We can see from the diagram that it is 3.

Regardless of the method that you chose to use to solve the problem. The answer should follow as:

5 + __ = 8 | 5 + 3 = 8

### Solving Unknowns in Subtraction Equations

**Example Problem: Find the unknown value in the equation: 7 - __ = 5**

**Math Based Solution**

**Step 1)** We can once again apply the mountain format. In this format we write the sum or difference at the top and the parts that create it at the bottom. In this case, 5 at the top (difference) and 7 and the unknown (noted by the blank square) at the bottom.

**Step 2)** Since the unknown is being subtracted from 7. We can count down from 7 until we hit our difference (5). In this case, it requires us to count down 2 times.

**Step 3)**This tells us our missing addend is 2.

### Solving Unknowns in Subtraction Equations

**Example Problem: Find the unknown value in the equation: 7 - __ = 5**

**Model Based Solution**

**Step 1)**You can also model this problem with the use of simple shapes. In this case, I will use a circle. We know the starting value is 7. As a result, we will draw 7 circles.

**Step 2)** The difference indicates a result of 5. We will model this by separating the last five circles. We then just need to count how many circles remain to make the total (7). We can see from the diagram that it is 2.

Regardless of the method that you chose to use to solve the problem. The answer should follow as:

7 - __ = 5 | 7 - 2 = 5