# Lesson 7

What is an Array?

## Warm-up: Which One Doesn’t Belong: Counter Collections (10 minutes)

### Narrative

This warm-up prompts students to carefully analyze and compare different arrangements of circles, including an array. Listen for the ways student describe how they see equal groups in each arrangement and use the language they developed in previous lessons to determine if a group of objects was even or odd.

### Launch

• Groups of 2
• Display the image.
• “Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
• 1 minute: quiet think time

### Activity

• 2–3 minutes: partner discussion
• Record responses.

### Student Facing

Which one doesn’t belong?

### Student Response

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### Activity Synthesis

• “How are the circles in B arranged differently than in the other groups?” (They are all lined up. They are arranged in rows. There are the same number of circles in each row. There are the same number of circles in columns, too.)
• “We call objects arranged in equal rows an array. The rows go from side to side. We are going to explore arrays today.”

## Activity 1: What is an Array? (20 minutes)

### Narrative

The purpose of this activity is for students to create arrays with counters. Students get sets of 6, 7, and 9 counters. Based on their experiences with images that show an even number of objects arranged in 2 equal groups, they may make an array with 3 rows and 2 columns or 2 rows and 3 columns with 6 counters. They may wonder if 7 or 9 counters can be arranged in an array since they are not even numbers.  Encourage students to experiment with other ways of arranging the counters that include more than 2 rows or columns. They may also make an array with 1 row. Arrays with 1 row or 1 column will be studied in future grades, so for the rest of this unit, students should be encouraged to make arrays with more than 1 row and more than 1 column.

### Required Materials

Materials to Gather

### Required Preparation

•   Create containers with 6, 7, and 9 counters for each group of 2.

### Launch

• Groups of 2
• Give each group 3 sets of counters with 6, 7, and 9.
• Display A from the warm-up or arrange counters to show:
• “The red counters are arranged in rows, but it is not an array. How could we rearrange the counters to make an array like image B?” (We could move the bottom two counters to the middle row. We could move one from the top row to the next row. We could move 1 from the third row to the bottom row.)
• 1 minute: quiet think time
• 1 minute: partner discussion
• Share responses.

### Activity

• “Arrange each of your sets of counters into an array. Your arrays should have the same number of counters in each row with no extra counters. Be prepared to explain how you made an array out of each set.”
• “If you have time, try to figure out a different way to make an array out of each set of counters.”
• 12 minutes: partner work time

### Student Facing

Arrange each set of counters into equal rows with no extra counters.

1. How many counters are there in all? _____

Show how you arranged them using words, drawings, or numbers.

2. How many counters are there in all? _____

Show how you arranged them using words, drawings, or numbers.

3. How many counters are there in all? _____

Show how you arranged them using words, drawings, or numbers.

### Student Response

For access, consult one of our IM Certified Partners.

If students create arrangements with unequal rows or only try to make arrays that have 2 rows or 2 columns (2 equal groups), consider asking:
• “What did you try so far? How many counters were in each row?”
• “_____ counters in each row did not make an array without any leftovers. What other amount of counters in each row could you try?”

### Activity Synthesis

• “7 and 9 are both odd numbers. What did you notice about the arrays you could make with them?” (I couldn't make an array with 2 rows. With 9 counters, I could do 3 rows with 3 counters in each row. For 7, the only way we did it was with 1 row with all 7 counters.)
• Display student work for array of 6 or arrange counters to show:
• “How can we describe this array of 6 counters?” (There are 3 on the top and 3 on the bottom.)
• “Another way to describe this array is to say there are 2 rows with 3 counters in each.”

## Activity 2: Rows of Counters (15 minutes)

### Narrative

The purpose of this activity is for students to describe the number of rows in an array, the number of objects in each row, and the total number of objects. They use this vocabulary to describe arrays and create arrays given a number of counters and a number of a rows (MP6). They may use trial and error to build these arrays.

This activity uses MLR8 Discussion Supports. Advances: speaking, conversing

Engagement: Provide Access by Recruiting Interest. Optimize meaning and value. Invite students to share ideas to create a context that relates to their own lives. For example, ask students where they have seen “arrays” in their world—eggs in a carton, cupcakes in a box, fruit organized at the grocery store, chocolates in a box, and so on.
Supports accessibility for: Conceptual Processing, Organization, Attention

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Arrange counters to show:
• “Which of these images shows 10 counters in an array? How do you know?” (The yellow counters are in an array because the rows have the same number of counters in each.)
• 30 seconds: quiet think time
• Share responses.
• “How many rows are in the array?” (2 rows)
• 30 seconds: quiet think time
• Share responses. Circle the 2 rows in the array.
• “How many counters are in each row?” (5 counters)
• 30 seconds: quiet think time
• Share responses.

### Activity

• “Now you will look at a few arrays to decide how many rows each one has, how many there are in each row, and the total number of counters. Then you will make arrays using counters.”
MLR8 Discussion Supports
• Display sentence frames to support students when they describe the structure of the array:
• “There are _____ rows in the array.”
• “There are _____ counters in each row.”
• “There are _____ counters in all.”
• 8 minutes: partner work time
• Monitor for students who build an array with 5 in each row for 20 counters.

### Student Facing

1. How many rows are in this array?
2. How many counters are in each row?
3. How many counters are there in all?

1. How many rows are in this array?
2. How many counters are in each row?
3. How many counters are there in all?
1. Use 6 counters to make 2 rows with the same number in each row. How many counters are in each row?
2. Use 20 counters to make 4 rows with the same number in each row. How many counters are in each row?

### Student Response

For access, consult one of our IM Certified Partners.

### Activity Synthesis

• Display student work for the array with 20 counters.
• “Describe _____’s array.” (It has 20 counters, it has 4 rows and 5 counters in each row.)
• “How can we prove there are 20 counters in this array?” (We can count them. We can skip count by 5. We can add $$5 + 5 + 5 + 5$$. The top 2 rows have 10 and the bottom 2 rows have 10.)

## Lesson Synthesis

### Lesson Synthesis

“Today you learned that an array is an arrangement of objects in rows with an equal number of objects in each row.”

Arrange counters to show:

“How could you use the rows to find the total number of counters?” (I know there are 3 rows with 5 in each row. I skip counted by 5. 5, 10, 15)

Share and record responses.

Record $$5 + 5 + 5 = 15$$

## Cool-down: Count the Counters (5 minutes)

### Cool-Down

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