Lesson 8 of 12
Objective: SWBAT explain why the order of two addends does not matter. (5+2 and 2+5)
Watch the youtube video below to see the start to this lesson. We started with the objective and then moved into a quick number sense routine. In just a couple of minutes, students explore combinations of 7, subitizing (knowing how many without counting) fingers patterns, and the commutative property. And they think it's so fun!
Today we are going to look at two problems to see if we can figure out the answer to our question today. Does it matter what the order of the two numbers is in an addition problem?
I sharpen 10 pencils. Then I sharpen 4 more pencils. How many pencils did I sharpen?
Partner talk guiding questions:
- What symbol do I need? What was the action of the problem?
- Do I have more or less pencils at the end?
- What number sentence could I write to match this story problem? (Leave answer blank)
I sharpen 4 pencils. Then I sharpen 10 more pencils. How many pencils did I sharpen?
Partner talk: How is this problem the same as the first problem? How is it different?
“Before we solve the problem, who thinks the answer for both problems will be the same? Who thinks the answers will be different? Let’s take a quick vote!”
Watch the youtube video below for the student share portion of this lesson. I model the 2 problems with student help.
After we figured out the answers were the same, I asked the following questions:
- Why are the answers the same?
- How does this show us the commutative property, or the flip flop?
Students solve 3 related fact story problems. The first 2 are addition facts (the commutative property) and the last one is a related subtraction problem for if students finish early.
The independent practice sheets are attached: IndPracticeCommutative.pdf. I left the numbers out so that you can write in the numbers that are most appropriate for your students! You can see how I created numbers for my differentiated math groups below.
- Group A: Intervention - I'll write in numbers under 10 for these students. I'll also make sure students model both problems with cubes to see that the total is the same.
- Group B: Right on Track - I'll write in numbers under 20 for students in this group. See the video below for how one student in Group B used counting on to solve!
- Group C: Extension - I'll write in numbers under 100 and on the decade for this group.
See this youtube video for how a few girls work together to figure out how to solve a problem using groups of 10!
Students summarize what they learned with a partner.
Focus Question: Show your partner your story problems. How were your story problems the same? How were they different?