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10.2 Area of Triangles, Parallelograms, Kites and Trapeziums

How do you estimate the area of various shapes?
LEARNING
STANDARDS
Various methods can be used to estimate the area of an
irregular shape. Estimate the area of
various shapes using
various methods.
(i) Using a grid with equal squares of sides 1 unit

✗ ✗
✗ ✓ ✓ ✓ ✓ ✗
✓ ✓ ✓ ✓ ✓ ✓ ✗ Number of full 1 unit squares (3 ) = 44
2
✗ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Number of half full or more than
✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✗
half full squares ( 7 ) = 10
✓ ✓ ✓ ✓ ✓ ✓ ✓
2
✓ ✓ ✓ ✓ ✓ ✓ ✓ Hence, the area of the shape is about 44 + 10 = 54 unit .
✓ ✓ ✓ ✓ ✓ ✗
✗ ✗

(ii) Drawing lines 1 unit apart

The lines are 1 unit apart from each other. Hence,
we can assume one line as a rectangle with a width
9 of 1 unit.
8
7
1 2 3
4 5 6 CHAPTER

Line 1 2 3 4 5 6 7 8 9 10
Length (unit) 4. 4 6.6 7.2 7.8 8.0 8.0 6. 4 5. 4 2.6

Area (unit ) 4. 4 6.6 7.2 7.8 8.0 8.0 6. 4 5. 4 2.6
2
= Length × 1 unit

Total area = 4. 4 + 6.6 + 7.2 + 7.8 + 8.0 + 8.0 + 6. 4 + 5. 4 + 2.6
= 56. 4 unit 2
2
Hence, the area of the shape is approximately 56. 4 unit .

Self Practice 10.2a

1. Collect some leaves from your school compound. Sketch the shape of each leaf on a
piece of paper. Then estimate the area of each leaf in cm , using suitable methods.
2

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Perimeter and Area

10 TB Math F1.indd 231 11/10/16 12:19 PM