Lesson 1.3 · Addition and Subtraction Facts
Arrays and repeated addition
Muffins in a pan, eggs in a carton, chairs in a room. Things are often lined up in neat rows. You can count them fast by adding the rows.
What is an array?
Definition
Array
An array is a group of objects in equal rows and equal columns. A row goes across. A column goes up and down.
This array has 3 rows. Each row has 4 stars.
⭐⭐⭐⭐
⭐⭐⭐⭐
⭐⭐⭐⭐
Add the rows
Each row has 4. Add 4 three times:
This is called repeated addition. You add the same number again and again.
Add the columns
You can count the columns instead. There are 4 columns with 3 stars each:
Same stars, same total!
Arrays and adding
To find the total in an array, add the number in each row, once for every row. Adding the columns gives the same total.
Worked example: Rows of apples
🍎🍎🍎🍎🍎
🍎🍎🍎🍎🍎
How many apples?
There are 2 rows of 5. . There are 10 apples.
Worked example: Skip count
Find the total. There are 4 rows with 3 dots in each row.
🔵🔵🔵
🔵🔵🔵
🔵🔵🔵
🔵🔵🔵
Count by 3s, once for each row: 3, 6, 9, 12. So . There are 12 dots.
Worked example: Draw an array
A pan has 5 rows of muffins. Each row has 2 muffins. How many muffins?
🧁🧁
🧁🧁
🧁🧁
🧁🧁
🧁🧁
. There are 10 muffins.
Common mistake
Add the number in a row, not the number of rows. For 3 rows of 4, write . Add one 4 for each row.
Tip
Skip counting is a fast way to do repeated addition. For 4 rows of 5, count 5, 10, 15, 20.
Practice
🌼🌼🌼
🌼🌼🌼
How many flowers are in this array?
Type a number.
⚽⚽⚽⚽
⚽⚽⚽⚽
⚽⚽⚽⚽
How many balls are in each row?
Type a number.
Which addition matches 3 rows with 5 in each row?
🟩🟩
🟩🟩
🟩🟩
🟩🟩
🟩🟩
🟩🟩
How many squares? (There are 6 rows of 2.)
Type a number.
What is ?
Type a number.
A garden has 3 rows of carrots. Each row has 5 carrots. How many carrots are in the garden?
Type a number.
Chairs are set up in 4 rows. There are 5 chairs in each row. How many chairs are there?
Type a number.