75
Units of area
Textbook: Part 3, lesson 75, pp. 22–24
GoalUnits of area: mm², cm², dm², m²; 1 dm² = 100 cm²; the area of a rectangle.
New words
area · yuz (maydon)square centimetre · kvadrat santimetr (sm²)square decimetre · kvadrat detsimetr (dm²)square metre · kvadrat metr (m²)
Explanation
The area of a shape is the number of unit squares that fit inside it. The unit squares have sides 1 mm, 1 cm, 1 dm or 1 m, and areas 1 mm², 1 cm², 1 dm², 1 m². A square with side 1 dm has 10 rows of 10 small cm² squares, so 1 dm² = 100 cm². In the same way 1 cm² = 100 mm² and 1 m² = 100 dm². The area of a rectangle = length × width (in the same unit).
Worked examples
3 dm² = 300 cm²; 4 dm² 25 cm² = 425 cm².
A rectangle with sides 8 m and 5 m: 8 × 5 = 40 m².
Class activity
“Tiling”: children draw a 1 dm² square (10 × 10 cm) on squared paper, count the 100 small squares inside, and find how many tiles would cover a given area.
Practice
1
7 dm² = ? cm²
700
2
2 m² = ? dm²
200
3
6 dm² 30 cm² = ? cm²
630
4
A plot is 9 m long and 4 m wide. What is its area in m²?
36
5
Square tiles with side 1 dm are fixed to a wall measuring 3 dm × 8 dm. How many tiles are needed?
24