An array is a set of objects in equal rows. Arrays are the first step toward multiplication, which you will learn in Grade 3 (Arrays). They grow out of Rows and Columns of Squares.
Why it works
Every row has the same number of objects, so you can add that number again and again, once for each row. Skip counting is a fast way to add equal numbers: 3, 6, 9, 12.
Worked example: 3 rows of 5
An array has 3 rows with 5 stars in each row. How many stars?
- Each row has 5.
- $5 + 5 + 5 = 15$. Or skip count: 5, 10, 15.
Answer: 15 stars
Worked example: Rows or columns
Show two ways to add an array with 2 rows of 4.
- Add the rows: $4 + 4 = 8$.
- Add the columns: there are 4 columns of 2, so $2 + 2 + 2 + 2 = 8$.
- The total is the same either way.
Answer: 8
Key idea
An array has equal rows. Add the equal rows (or columns), or skip count, to find the total.
Common mistake
Counting every object one by one. It works, but it is slow and easy to lose your place. Add the rows instead: 4 rows of 3 is $3 + 3 + 3 + 3$. Check by adding the columns, too.
Grown-up tip: Look for arrays in egg cartons, muffin pans and windows, and add them by rows.