Step by step
The question
Question: find the area of this L-shape: 20 m by 15 m, with a 8 m by 6 m corner cut out.
1 Split into rectangles
This shape is not a rectangle.
One line cuts it into two rectangles.
We call them top and bottom.
2 Find the missing sides
The top side is the whole 20, take away the 8 cut out.
20 minus 8 is 12.
20 − 8 = 12
The right side is the whole 15, take away the 6 cut out.
15 minus 6 is 9.
15 − 6 = 9
3 Area of each part
The top rectangle is 12 by 6.
12 times 6 is 72.
top = 12 × 6 = 72 m2
The bottom rectangle is 20 by 9.
20 times 9 is 180.
bottom = 20 × 9 = 180 m2
4 Add the parts
The whole area is the two parts added.
A = 72 + 180
72 plus 180 is 252.
So the area is 252 m².
A = 252 m2
5 Check
Let's check another way: the whole 20 by 15 rectangle, take away the corner.
20 × 15 − 8 × 6 = 300 − 48 = 252
We get 252 again.
So the area is right!
Let's look back.
First: split into rectangles.
Then: find the missing sides.
Then: area of each part.
Then: add the parts.
Last: check.
Answer
A = 252 m2