# Relationship between Addition & Subtraction

Determining the relationship between addition and subtraction is a first grade, Common COre math skills: 1.OA.3. 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 pairs 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, the 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.3 - Applying properties of operations as strategies to add and subtract

Students who understand this principle can:

1. Represent addition and subtraction problems in various ways.
2. Understand and describe addition and subtraction properties and strategies.
3. Demonstrate or explain their thinking.

Video 1: Adding and Subtracting Strategies

The video, narrated by the number 1 in a tie, starts by visualizing addition by counting yellow and blue rubber duckies. There are three blue ducks and seven yellow ducks, so 3 + 7 = 10 ducks. It then switches the order of the blue and yellow ducks and shows that the answer (10) is still the same.

Only in addition, there is the Commutative Property: The order of numbers can be switched as many times as you want and the answer remains the same.

The video then presents a series of practice math problems for your students to practice what they just learned. However, there is a mix of addition and subtraction.

1. If 8 + 2 = 10, then __ + 8 = 10.
a. So,  2 + 8 = 10
2. If 9 - 4 = 5, then 9 - 5 = __
a. Subtraction does not work like addition, but the two are similar.
b. Uses a “math mountain” to demonstrate this idea.
i. At the top is the total, at the bottom are “partners” or “addends.”
ii. You can add the partners to get the total, and subtract the total from one of the partners to find the other partner.
c. So, 9 - 5 =  4 :)
3. If 2 + 6 + 4 = 12 is the same as 10 + __ = 12
a. Making groups of doubles or tens is helpful in situations like this.
b. Adding 6 and 4 makes 10.
c. So, 10 + 2 = 12

Video 2: Adding and Subtracting Cupcakes

The video follows Jen as she tries to bake the proper number of cupcakes for herself and her friends. Knowing that 7 friends were coming, she baked 7 cupcakes, then she baked one more for herself. Boddle asks how many cupcakes she baked in total.

1. First, 7 cupcakes are counted.
2. Next, the 1 cupcake is added to the 7, ending with 8.
a. 7 + 1 = 8

The situation is flipped, and Jen bakes one cupcake first and then 7 for her friends.

1. So now, 1 + 7 = 8. She still baked 8 cupcakes.
2. 7 + 1  and 1 + 7 are the same in addition.

Later, Jen eats her cupcake before her friends arrive because she is hungry. The video asks how many cupcakes she has left.

1. There were 8 cupcakes, but Jen ate one.
2. 8 - 1 = 7.

The situation is reversed; this time all her friends eat their cupcakes, but she does not eat hers.

1. So now, 8 - 7 = 1

During the lesson, your students have made a Fact Family. A Fact Family is made of only 3 numbers: 8, 7, and 1. In the lesson, two addition and two subtraction equations are made.

Want more practice?