A composite shape is made of simpler shapes joined together. For an L-shape, make one straight cut to split it into two rectangles. Find the area of each rectangle (length × width) and add them. Make sure the rectangles do not overlap. Another way is to find the area of the big rectangle around the shape and take away the missing corner. If some sides are not labelled, work them out first from the sides you know.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- composite shape
- a shape made by joining simpler shapes
- square metre (m²)
- the area of a square 1 m long and 1 m wide
Worked examples
An L-shape is split into a 6 m by 3 m rectangle and a 10 m by 5 m rectangle. What is its area?
- 1.6 × 3 = 18 and 10 × 5 = 50.
- 2.18 + 50 = 68 m².
= 68
An L-shape is a 12 m by 9 m rectangle with a 5 m by 4 m corner cut out. What is its area?
- 1.Whole rectangle: 12 × 9 = 108. Cut-out: 5 × 4 = 20.
- 2.108 − 20 = 88 m².
= 88
An L-shape has outer sides of 10 m and 8 m. The shorter sides beside the cut-out corner are 6 m and 5 m. What is its area?
- 1.Missing sides: 10 − 6 = 4 and 8 − 5 = 3.
- 2.10 × 8 = 80, 4 × 3 = 12, 80 − 12 = 68 m².
= 68
For parents
Method: Split into rectangles
What to say: Where could you cut this into rectangles? Do the rectangles overlap?
Common mistakes:
- Multiplies the two longest sides, ignoring the corner that has been cut out.
- Splits the shape into two rectangles that overlap, so part of the area is counted twice.
- Adds the side lengths (the perimeter) instead of finding the area.