Grade 3 · Maths · Lessons
Splitting the rectangle
✂️cut🟦left part🟩right part➕add
Split a shape.The big ideaCut a shape into rectangles. Find each area. Add the areas.
How it works
Cut a shape into rectangles. Find each area. Add the areas.
A rectangle 4 by 8 can be cut into 4 by 2 and 4 by 6.
The two parts add to the whole.
Example 1: Two parts
- A rectangle is 4 rows of 8. Cut it after 2 columns.
- The left part is 4 × 2 = 8. The right part is 4 × 6 = 24.
- 8 + 24 = 32, and 4 × 8 = 32.
Example 2: A missing part
- 2 times 5 is 2 times 2 plus what?
- 2 × 5 = 10 and 2 × 2 = 4.
- 10 − 4 = 6, so it is 2 times 3, which is 6.
Example 3: An L shape
- Cut an L shape into two rectangles, 3 by 8 and 2 by 4.
- 3 × 8 = 24 and 2 × 4 = 8.
- 24 + 8 = 32 square units.
Words to know
- split
- To cut into parts.
- rectangle
- A shape with four square corners.
Watch out
- Cut along a straight line.
- Add the areas of the parts.
- Check against rows × columns for the whole.
Try it
- A 3 by 6 rectangle is cut into 3 by 2 and 3 by 4. What are the two areas?
- What is the total of those two areas?
- Does it match 3 × 6?
- What do you do with the areas of the parts?
Answers: 1. 6 and 12 · 2. 18 · 3. yes · 4. add them
For grown-upsDraw a rectangle on squared paper and cut it with a line. Work out the area two ways.