Lesson 3

Sharing Cookies

Est. Class Sessions: 2

Developing the Lesson

Part 1: Partitioning Numbers into Groups

Read The Doorbell Rang. The Doorbell Rang by Pat Hutchins is an effective introduction to partitioning numbers into groups. The story involves sharing one dozen home-baked cookies among different numbers of children so that each one gets a fair share. Read the story to the students.

As you read, ask students to think about ways to share the cookies:

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  • In the story each child received a fair share of cookies. What do you think it means to get a fair share? (Possible answer: A fair share is when each person gets the same number.)
  • Why should you give each child the same number of cookies? (Possible answer: It’s not fair if one person gets nine cookies and the other one gets three cookies.)
  • At the beginning of the story, Sam and Victoria said they would each get six cookies. How did they know that the two children should get six cookies each? (12 cookies shared by 2 children is 6 cookies each.)
  • If each child gets one plate, how many plates will you need? (2)

Share 12 Cookies. Give each student pair twelve counters and 12 small paper plates. Direct students to look at Question 1 on the Sharing 12 Cookies page in the Student Activity Book. Reread the story, this time pausing each time a different number of children rings the doorbell. Have student pairs use their plates to show the number of children sharing and their counters to show the number of cookies in each child’s share. Ask students to record their work on the plates in Question 1. See Figure 1. Emphasize the importance of giving each child a fair share.

As students are working in pairs, monitor students to see what strategies they are using. If students are unable to find a strategy for solving partitioning problems, encourage them to try the strategy of passing out one cookie at a time until all the cookies have been shared.

Ask:

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  • What are some of the strategies you used to solve this problem?
  • What number sentence could we write for this problem?
  • When do you have fewer cookies on each plate? (when you have to share them with more people)

Possible strategies students might use include:

  • Guessing the number of cookies in each share, checking to see if it is correct, then adjusting the number in each share so that each child gets the same number.
  • Passing the cookies out by a given number such as two or three cookies at a time and making adjustments so that each child gets a fair share.
  • Using addition to determine the number of cookies in each fair share. (6 + 6 = 12)
  • Passing out one cookie at a time until all the cookies have been shared.

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Students often confuse the number of children and the number of cookies each child receives. For example, if there are two children and 12 cookies, they might place two in each group and say that each child gets two cookies. To clarify the problem, ask:

  • How many children are there? (2)
  • How many plates do you need to show the number of children? (2 plates)
  • How many cookies are there? (12)
  • Place the 12 cookies evenly on the two plates until all the cookies are shared. Encourage students to distribute cookies one at a time until they run out of cookies. This should demonstrate to students that they are not placing 2 cookies on each plate or there will be too many cookies left over.
Remind students that they are telling you the number in each fair share and not the number of children who are sharing the cookies.

For each problem, have several students share their work with the class to highlight the different strategies students can use to partition numbers.

ADVENTURE BOOK:
Student Activity Book: 97
Answers
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SG_Mini
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Master:
Sharing twelve cookies among two, four, six, and 12 children
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