operations · Year 2 · AC9M2N05
Multiply and divide with arrays
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.
Sample questions
An array has 2 rows with 2 stickers in each row. How many stickers are in the array altogether?
- Each row has 2. Use repeated addition: 2 + 2.
- Check by counting the columns: 2 columns of 2.
- 2 × 2 = 4.
Answer: 4
An array has 5 rows with 5 shells in each row. How many shells are in the array altogether?
- Each row has 5. Use repeated addition: 5 + 5 + 5 + 5 + 5.
- Check by counting the columns: 5 columns of 5.
- 5 × 5 = 25.
Answer: 25
An array has 4 rows with 4 stars in each row. How many stars are in the array altogether?
- Each row has 4. Use repeated addition: 4 + 4 + 4 + 4.
- Check by counting the columns: 4 columns of 4.
- 4 × 4 = 16.
Answer: 16