An array has objects in equal rows. To find how many, add the row again for each row, or skip count by the row size. 4 rows of 5 is 5 + 5 + 5 + 5, which is 20. To divide, undo this. If 20 are in 4 equal rows, count one row to find 5 in each row. To put 20 into groups of 5, skip count by 5 to 20 and count the numbers: 4 groups. In a two-step problem, find the array total first and then do the change.
Explore this idea with maths tools
Equal groups
3 × 4 = 12
12 ÷ 3 = 4
The same picture shows multiplication and division. Each group must have the same number.
Words to know
- array
- objects arranged in equal rows and columns
- repeated addition
- adding the same number again and again
- equal groups
- groups that all have the same number
Worked examples
An array has 4 rows with 5 stars in each row. How many stars altogether?
- 1.Each row has 5.
- 2.Repeated addition: 5 + 5 + 5 + 5 = 20.
- 3.4 × 5 = 20.
= 20
Put 24 shells into groups of 4. How many groups can you make?
- 1.Skip count by 4 until you reach 24: 4, 8, 12, 16, 20, 24.
- 2.You said 6 numbers.
- 3.So 24 ÷ 4 = 6 groups.
= 6
The array shows 3 rows of 4 marbles. 2 more rows of 4 are added. How many marbles are there now?
- 1.There are 3 + 2 = 5 rows of 4 now.
- 2.Skip count by 4: 4, 8, 12, 16, 20.
- 3.5 × 4 = 20.
= 20
For parents
Method: Use repeated addition or skip counting on equal rows.
What to say: How many rows? How many in each row? Are you finding the total, or one row?
Common mistakes:
- Adds the number of rows to the number in each row instead of using equal groups.
- Gives the number in one row or group instead of the whole.
- Skip counts one row or group too few.
- Finds the array total but does not do the final step of the story.
- Mixes up the number of rows (or groups) with the number in each row.
- Gives the total number of objects instead of the share or number of groups.
- Takes the group size (or number of rows) away from the total instead of dividing.
- Adds the objects taken away when the story says they are taken away.