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Lesson 1.4

The Size of the Group . Lesson 1.4. Array Multiplication . For each array, say the repeated addition multiplication equation. Application Problem . The student council holds a meeting in Mr. Chang’s classroom. They arrange the chairs in 3 rows of 5. How many chairs are used in all?

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Lesson 1.4

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  1. The Size of the Group Lesson 1.4

  2. Array Multiplication • For each array, say the repeated addition multiplication equation.

  3. Application Problem • The student council holds a meeting in Mr. Chang’s classroom. They arrange the chairs in 3 rows of 5. How many chairs are used in all? • Use the RDW process. • Read • Draw • Write

  4. Application Problem • Solution

  5. Guided Instruction: Concrete to Abstract • Yesterday our neighbor Mr. Ziegler bought a new pack of 18 markers. He wanted to share them with me, so this morning he divided them into 2 equal groups. Now I have a bunch of new markers for making our charts! Do you want to know how many he gave me? • What are we trying to find, the number of groups or the size of the group? • Your 18 counters represent the markers. Divide your 18 counters into__ equal groups, by giving one to Mr. Z, one to me, one to Mr. Z, one to me (model the partitioning.) • Using a complete sentence, tell how many counters are in each group.

  6. Guided Instruction: Concrete to Abstract • Then how many markers did Mr. Ziegler give me? • Write a number sentence to show our work, starting from the beginning. What is our total number of counters? • We divided our 18 counters into how many equal groups? • 18 ÷ 2 = ____ • If 18 is our total and 2 represents our equal groups, then remind me, what does our unknownfactor represent? • This equation shows that Mr. Z gave how many markers?

  7. Guided Instruction: Concrete to Abstract • “Suppose Mr. Z had 15 markers and shared fairly with 2 teachers?” • What does ÷ mean? • In what ways does dividing remind you of our work with multiplication? • It’s about the size of groups and the number of groups, but we used a different symbol. • It still uses factors and a total. • This time the total is not the answer. It’s the beginning! • The answer has to do with groups, not the total.

  8. Guided Instruction: Concrete to Abstract • We multiply when we want to find the total. Here, we divided when we knew the total and wanted to find the size of the groups. • 15 ÷ 3 = ___

  9. Guided Instruction: Pictorial to abstract • This is how Diana arranges her star stickers. • What does the 12 represent in the picture? • What does the 3 represent? • What does the 4 represent? • Write an equation to represent Diana’s stickers where the answer represents the size of the group.

  10. Guided Instruction: Pictorial to abstract • 12 ÷ 3 = 4 12 ÷ 4 = 3 • What is the difference between these division sentences? • If we’re writing a division sentence where the answer represents the size of the group, then which equation should we use? • 12 ÷ 3 = 4

  11. Guided Instruction: Abstract to pictorial • 8 ÷ 4 = ___ • If 8 is the total and 4 is the number of groups, then what does the unknown factor represent? • The size of the groups • Draw a picture on your board to go with my division sentence. Use your picture to help you find the unknown factor, then write the complete equation. • Students share pictures to go with 8 ÷ 4 = 2.

  12. Guided Instruction: Abstract to pictorial • 10 ÷ 2 = ____ • If 10 is the total and 2 is the number of groups, then what does the unknown factor represent? • The size of the groups • Draw a picture on your board to go with my division sentence. Use your picture to help you find the unknown factor, then write the complete equation. • Students share pictures to go with 10 ÷ 2 = 5.

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