Our Strategies for Result Unknown Problems

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SWBAT solve result unknown problems using their own strategies.

Big Idea

Students identify, use, and share their strategies for result unknown word problems.


10 minutes

 We are going to act out a  practice problem.  I need a volunteer!   Last weekend, ________ (student name) ate 251 M&Ms. (ask student to pretend to eat M&Ms very quickly!)   I have the student stand up and give him or her a white board with “251 M&Ms” written on it.  Then, a little later, _________ ate  651 M&Ms.  I hand the student another white board that says 651 on it. 

Ask students:  during the weekend, __________ ate 251 M&Ms and then ______ ate 651 M&Ms.  What strategies can we use to determine how many M&Ms he ate during the weekend? 

Students will likely suggest to add the two numbers but make sure to ask them WHY.  For students who are struggling to explain why they should add have the visual of the student holding two white boards help them—this person ate 251 M&Ms and then 651 M&Ms, so we add them up to determine a total


Introduction to New Material

10 minutes

You just solved a change unknown using three digit numbers!  Now we are going to work on a similar problem of the day.  I write the following problem of the day on the board:

_______ has 372 rocks in his rock collection.  His mom gives him 115 more. How many does he have now? 

 Before beginning, I want you to turn toyour partner and share how you plan to solve this problem and why.  

As students discuss, I circulate to listen for strategies or any common misconceptions.

 Now that you have shared, I want you to solve this problem on your white board.

When students have finished working ask two-three students to share their work. Make sure that you are picking students who used different strategies (i.e: 372 + 115= ____ OR _____- 372 = 115) to set this problem up and different strategies to solve it (regrouping, tens and ones, etc.)

As students share their strategies, model those strategies on the board using mathematical symbols so that students will have a visual reminder of some of the strategies their teammates used.





Guided Practice

10 minutes

Now you are going to have a chance to work with a partner to solve one of these problems.  Use the strategies that we have discussed to solve this problem accurately.


I hand out the guided practice worksheets to students and have them work in heterogenous pairs so that they can support each other in answering the question and finding appropriate strategies.


When students have finished, I bring them back together and have them share their strategies (ask 2-3 pairs to share--choose students who have chosen different strategies).  As students present, ask them:

Why did you choose that strategy?

Explain how that strategy works. 

Why did you choose to ___________ in this problem?


If students are all struggling with one component (regrouping, choosing an appropriate strategy or operation), use this time for necessary re-teaching.  If not, release students to the independent practice. 


Independent Practice

15 minutes

Independent practice is tiered by understanding of this concept. During the independent practice, I will circulate starting with group A, moving to group B, and ending with group C.  

 I group students based on their mastery of the exit ticket from yesterday's lesson, their performance during the guided practice problem, and their general mathematical understanding (i.e: can they regroup or not?) 

Group A: In need of intervention

Students will work on change unknown problems using 3 digit numbers 100-500 (NO REGROUPING). 


Group B: Right on track! 

Students will work on change unknown problems using 3 digit numbers 100-800 (SOME REGROUPING). 


Group C: 

Students will work on change unknown problems using 3 digit numbers 100-1000 (SOME REGROUPING). 


5 minutes

Today we found and shared our strategies for solving change unknown word problems. In your math journal, write about what we learned today and how you will continue to use your strategy. 

I use math journals as a reflection tool--students write reflections about what they learned and keep records of the strategies they have developed. Encouraging students to write about their strategies and reflect upon what they have learned helps students to internalize their strategies.