Introduction to Four Addends

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Objective

SWBAT add four two-digit numbers to find a sum.

Big Idea

In this lesson, students identify strategies to add four two-digit numbers together.

Introduction/Hook

10 minutes

I put the problem of the day on the board. 

James has 23 orange skittles, 39 red skittles, 26 green skittles, and 19 yellow skittles.  How many skittles does he have in all?

Turn and talk:  What operation should we use to solve this problem? 

Students will likely indicate that they should add all four together because we want to figure out how many total skittles there are.  If students are struggling to determine how to set up the problem, I give them paper or a white board to draw out the problem.  Drawing the problem enables them to visualize the problem more clearly.  

After students have discussed which operation to use for about one minute, I bring the class back together and ask one or two students to share which operation they chose and WHY.  I use these guiding questions to prompt student discussion (1) How do you know you should add?  (2) What clues does the story problem give us to tell us we should add?  

Turn and Talk: Now, I want you to tell me how you think we should solve this problem?  What strategies should we use?  

If students simply say “we need to add the four together” push them to explain HOW they will add the four together. 

After students share out their ideas have students work in groups to solve this problem—give students  white boards, white board markers, cubes and place value blocks to help them solve the problem as necessary. 

Some students may add all four numbers up, others may draw tens or ones, others may add two of the addends together, then add the next two, and then add the two sums. As students work, ask them guiding questions: Why did you choose this strategy?  How do you know that this strategy will work? 


Introduction to New Material

10 minutes

After students have worked to solve the problem, I have two groups come forward to model how they solved it.  Students may share that they used 10s and 1s to solve the problem or that they stacked all four and then regrouped.  Some students may model how they used cubes to add all four together.  Other students may have used an open number line to efficiently add the four numbers. 

As students share their strategies, record them on an anchor chart or on the board.  After students have finished sharing, post the following image on the board.

Today I am going to do a strategy spotlight where I model a strategy that I saw students working on during our problem of the day. 

When my friend  had to add four numbers together they started by adding two numbers together using a regrouping strategy (model adding the first two together in one of the upper circles),  Then, he/she added the two other numbers together using the regrouping strategy (model adding the first two together in the other upper circle).  Then he/she needed to add the two sums together. He/she added the two sums together in the lower circle.   

 I chose to spotlight this strategy because several of my students chose to add all four numbers together using column addition.  When they added all four numbers using column addition, I noticed their accuracy was off.  This strategy allows students to continue to practice their regrouping skills if they are comfortable.  If one of your students does not come up with this specific strategy during the introduction to new material, you can either pick a different student strategy to spotlight or use this strategy--don't label it as "your" strategy, though, since students will likely mimic it and not take the time to develop a conceptual understanding of this skill. Read more about strategy spotlights in the linked reflection. 

Guided Practice

10 minutes
Now that we have shared our strategies as a group, you are going to work by yourself to solve a problem similar to our whole class problem.  You can use any strategy that will help you get an accurate answer. 

I distribute the guided practice problem as well as cubes and place value blocks for students who want to use them.  As students work, I circulate and ask guiding questions:
1)What strategy are you using?
2) What steps are you taking to make sure your work is accurate?
3) What number sentence matches the story problem?
 
After students have had time to complete the problem, I have all of the students come back together and have students share their strategy, why they chose that strategy, and how they solved the problem. As students present, I ask them: Why did you choose that strategy? Show the class how this strategy works...,  Explain how you check your work in your strategy...  If students used place value blocks or cubes to solve, I have them model using these manipulatives so that their teammates can clearly see how their strategy works.   
When finished, I ask students to turn and talk: How are the strategies shared similar or different from the strategy that you worked on? 
This activity allows students to critique the reasoning of others (MP3) and learn new strategies for solving multiple addend problems. 

Independent Practice

10 minutes

Independent Practice is differentiated by mathematical understanding of this skill" 

Group A: In need of intervention

This group will work on adding four addends using numbers 10-30 that will not require them to regroup into the hundreds.  In this group, students should be focusing on using tens and ones or only adding two addends at once in order to get an accurate answer.  Place value blocks and cubes will be available to this group. 

Group B: Right on Track! 

This group will work on adding four addends using numbers 20-60.  Place value blocks and cubes will be available to this group. 

NOTE: On the worksheet the numbers for group A and B are left blank so that you can fill in appropriate numbers for your groups. The numbers I've provided are suggestions based on what worked with my groups.

Group C: Extension

This group will work on adding FIVE addends using numbers 20-100.  Place value blocks and cubes will be available to this group, but many students will be able to solve these problems more abstractly by regrouping or using an open number line.  

 

Exit Ticket

5 minutes

Now that you have worked on these kind of problems in groups and alone, it's time for you to show me what you know!  

Hand out the exit ticket and allow students to take it quietly with our without manipulatives.