Making Arrays
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An array is a special way to organize objects in rows and columns. Arrays help us count things quickly and get ready for multiplication!
What Is an Array?
An array is a group of objects arranged in equal rows and equal columns, like a rectangle.
Think of eggs in a carton, muffins in a pan, or seats in a classroom!
Rows and Columns
- Rows go across (left to right), like rows of desks in a classroom
- Columns go up and down (top to bottom), like columns on a building
Here is a 2 by 3 array (2 rows, 3 columns):
* * *
* * *
How to Describe an Array
We describe arrays by their rows and columns:
- A "3 by 4" array has 3 rows and 4 columns
- We write it as: 3 x 4
- The first number is always the rows!
Why Arrays Are Useful
Arrays help us:
- Count large groups quickly
- See equal groups clearly
- Get ready for multiplication in Grade 3!
Worked Examples
Example 1: Describe this array
* * * *
* * * *
* * * *
Step 1: Count the rows (going across): 3 rows
Step 2: Count the columns (going down): 4 columns
Answer: This is a 3 by 4 array (3 x 4)
Example 2: How many stars in total?
* * *
* * *
Step 1: This is a 2 by 3 array
Step 2: Count the stars in each row: 3 stars per row
Step 3: There are 2 rows: 3 + 3 = 6
Answer: There are 6 stars in total
Example 3: Make an array
Problem: Draw a 4 by 2 array
Step 1: 4 by 2 means 4 rows and 2 columns
Step 2: Draw 4 rows with 2 objects each:
* *
* *
* *
* *
Answer: A 4 x 2 array has 8 objects total!
Example 4: Real-world array
Problem: A muffin tin has 2 rows with 6 muffins in each row. How many muffins can it hold?
Step 1: This is a 2 by 6 array
Step 2: Count: 6 + 6 = 12
Answer: The muffin tin holds 12 muffins
Example 5: Same array, different view
Problem: Is a 2 by 5 array the same as a 5 by 2 array?
2 by 5:
* * * * *
* * * * *
5 by 2:
* *
* *
* *
* *
* *
Answer: They look different, but both have 10 objects! Turning an array on its side gives you the same total.
Practice Problems
Try these problems on your own. Click "Show Answer" to check your work!
Problem 1: How many rows in a 3 by 5 array?
Show Answer
3 rows (The first number tells you the rows)
Problem 2: How many columns in a 4 by 3 array?
Show Answer
3 columns (The second number tells you the columns)
Problem 3: Describe this array:
* * * * * * * * * * * *
Show Answer
4 by 3 array (4 rows, 3 columns)
Problem 4: How many objects are in a 2 by 4 array?
Show Answer
8 objects (4 + 4 = 8, or 2 + 2 + 2 + 2 = 8)
Problem 5: A window has 3 rows of panes with 2 panes in each row. How many panes total?
Show Answer
6 panes (2 + 2 + 2 = 6)
Problem 6: How many objects are in a 5 by 2 array?
Show Answer
10 objects (2 + 2 + 2 + 2 + 2 = 10)
Problem 7: An egg carton has 2 rows with 6 eggs each. Describe the array.
Show Answer
2 by 6 array with 12 eggs total
Problem 8: How many objects are in a 3 by 3 array?
Show Answer
9 objects (3 + 3 + 3 = 9)
Problem 9: A chocolate bar has 4 rows with 3 squares in each row. How many squares?
Show Answer
12 squares (3 + 3 + 3 + 3 = 12)
Problem 10: Is there a difference between a 1 by 5 array and 5 objects in a line?
Show Answer
No! A 1 by 5 array is just 5 objects in one row - the same as a line of 5!
Check Your Understanding
Question 1: What is an array?
Show Answer
An array is a group of objects arranged in equal rows and equal columns, forming a rectangle shape.
Question 2: In "4 by 6", which number tells you the rows?
Show Answer
4 - The first number always tells you the rows.
Question 3: Why are arrays useful for counting?
Show Answer
Arrays help us count quickly because we can add equal groups instead of counting one by one.
Question 4: Name something in real life that looks like an array.
Show Answer
Examples: egg carton, muffin tin, window panes, tiles on a floor, seats in a theater, stamps on a sheet, keys on a keyboard, chocolate bar squares.
Next Steps
- Look Around: Find arrays in your home and classroom
- Draw: Practice drawing different arrays with stickers or stamps
- Next Lesson: Learn about repeated addition to count arrays faster!
- Preview: Arrays will help you learn multiplication in Grade 3!