Perimeter and Area
Solve practical problems involving the perimeter and area of regular and irregular shapes using appropriate metric units.
Read this first
Perimeter is the distance around. Area is the space inside.
Around the edge is 16 cm. Inside there are 15 squares.
Words you need
- Perimeter
- The distance all the way around.
- Area
- The amount of space inside.
- Square unit
- A square that is 1 unit on each side.
Worked example
e.g. Find the perimeter and area of a rectangle 5 cm by 3 cm.
- For perimeter, add every side. 5 + 3 + 5 + 3.
- That gives 16 cm.
- For area, count the squares inside.
- There are 5 rows of 3, so 15 square centimetres.
Perimeter uses cm. Area uses square cm. The units are different.
Practice
The pictures fade as you go. By the last few you are on your own.
1Find the perimeter of a 4 cm by 2 cm rectangle.with a picture
Answer12 cm.
2Find the area of a 4 cm by 2 cm rectangle.with a picture
Answer8 square cm.
3A square has sides of 6 cm. Find its perimeter.with a hint
Need a hint?
All four sides are the same.
Answer24 cm.
4A shape is made of 7 whole squares and 2 halves. Find the area.with a hint
Need a hint?
Two halves make one whole.
Answer8 square units.
5Find the area of a square with sides of 5 cm.on your own
Answer25 square cm.
6Two rectangles both have area 12. Must they have the same perimeter?on your own
AnswerNo. 3 by 4 and 2 by 6 are different.
7Why does area use square units?on your own
AnswerYou are counting squares, not lengths.
Think about it
1
Can two shapes have the same area but different shapes?
One good answerYes. 1 by 12 and 3 by 4 both have area 12.
2
What happens to the perimeter if you double every side?
One good answerIt doubles too.
Common mistakes
Adding only two sides for perimeter.
A rectangle has four sides. Add them all.
Using cm for area.
Area is counted in square cm.