George and Martha: Missing Parts

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SWBAT solve the missing part of a 3 addend equation.

Big Idea

Connect to a classic children's story and extend student thinking! Students apply their understanding of 3 addend equations to solve for the missing part of a story problem.

Hook & Objective

10 minutes

Read Aloud: I will have already read the story of Split Pea Soup from the original George and Martha by James Marshall. If you haven't read this to your children yet, you can read it at the beginning of the lesson, which means the lesson will take you a bit longer than I have planned here!

Review and Connect:

We have been working with number sentences that have 3 addends. Today we are going to use what we know about 3 part number sentences and apply that to figure out the missing parts.


Your thinking job is: What strategy can I use to figure out the missing part?


Opening Discussion

10 minutes

Present problem:

George and Martha are buying the ingredients for Split Pea Soup. They buy 8 carrots, 2 onions and some potatoes. They buy 13 vegetables in all. How many potatoes did they buy?

Guiding Questions: These questions help students internalize the kind of thinking they need to do to "Make sense of a problem" (MP3). With enough practice, students start asking themselves these questions!

  • Retell the story to a partner.
  • What part of this story problem is missing?
  • What is the 13 telling you?
  • Partner talk: How do you plan to solve it? Watch a video of one student planning out her strategy. You'll see that she is already thinking about number combinations and counting strategies. 

I'll have 2-3 students share out their plan to solve, just to get kids warmed up for this kind of thinking.

Student Work Time and Share

25 minutes

Work Time:

I'll give students 7-10 minutes to solve and write about their solution. During this time, I am floating looking for different strategies. I'll choose 3 strategies to share. The strategies I am looking for are (from least to most sophisticated)

1. Student uses cubes/drawings to represent the given information, then takes out more cubes until they get to 13.

2. Students use counting to help them solve. They start at 8, count on 2, then count on to 13 to figure out the missing part.

3. Students use known facts. They immediately add 8 and 2 to make 10. Then they use the known fact 10 + 3 to help them solve.

    • Watch a video of one student who used known facts! She also applied knowledge of base 10, which is really exciting. 


Student Share:

First, I'll have students share their strategies at their desks with their math partners. This insures that every student gets a chance to practice MP3, "Construct viable arguments and critique the reasoning of others. 

This section gives students the opportunity to teach each other and give each other feedback on how they did. Watch a video of one partner discussion: The little girl holds firm to disagreeing with the student she is working with!

Students come back together and I have each student leader share the strategy they used. After each student share, I'll have students turn and talk and share how that person solved that problem.

Other focus questions:

  • How is this strategy different?
  • How did each person figure out the 3 missing vegetables?
  • Which tool helped us figure out the missing part the fastest?

Independent Practice

15 minutes

Students solve George and Martha story problems. For most students, they will solve story problems with sums under 20.

For students who need intervention or an extension, I included problems that do not have the numbers in them. You can write in the appropriate numbers for your students!


For my intervention students, I will make the sums under 12.


For my extension students, I will continue to encourage 50 as a landmark number.

Number example: 45, 5 and 10.

Story problems are attached!


5 minutes

Students choose their best work to share with a partner! This gives students practice with MP3, Construct viable arguments; students get practice explaining their reasoning clearly to a peer!