You can cut a rectangle into rows and columns of same-size squares, like a sheet of stamps or a pan of corn bread. You know about rectangles from Shapes by Sides, Angles and Faces.
Why it works
Rows go across and columns go up and down. The squares are all the same size and line up, so every row has the same number of squares. That means you can add the rows instead of counting one by one: $4 + 4 + 4 = 12$.
Worked example: 2 rows of 5
A rectangle has 2 rows with 5 squares in each row. How many squares?
- Each row has 5.
- $5 + 5 = 10$.
Answer: 10 squares
Worked example: 3 rows and 3 columns
A rectangle has 3 rows and 3 columns of squares. How many squares?
- 3 columns means each row has 3 squares.
- $3 + 3 + 3 = 9$.
Answer: 9 squares
Key idea
A rectangle cut into same-size squares has equal rows. Add the rows (or the columns) to find how many squares there are.
Common mistake
Drawing squares that are not all the same size. For rows and columns to work, every square must match. Check: do the lines go straight across and straight down, evenly spaced?
Grown-up tip: Draw a rectangle on graph paper and cut it into squares together, then count them by rows.