Page 235 - ICSE Math 8

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¾ Area of a trapezium = × (sum of the lengths of its parallel sides) × height
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¾ To find the area of a regular or irregular polygon, we divide it into triangles, trapeziums, parallelograms,
etc., and find the area of each figure. The area of the polygon is equal to the sum of these area.
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¾ Circumference of a circle = 2πr and area of a circle = πr , where r is the radius of the circle and
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π = 7 or 3.14

MENTAL MATHS

1. Fill in the blanks.
(a) The adjacent sides of a parallelogram are 12 cm and 18 cm. Its perimeter is ___________.
(b) The circumference of a circle of radius 7 m is ___________.
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(c) The length of a rectangle with area 352 cm and breadth 16 cm is ___________.
(d) The ratio between the circumference and diameter of a circle is represented by ___________.
2. Write True or False.

(a) Each diagonal of a parallelogram divides it into two congruent triangles.
(b) Area of a rhombus is equal to the product of its diagonals.
(c) Perimeter of a circle is the length of the entire arc of the circle.
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(d) The area of an equilateral triangle with side a units is a square units.
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(e) The length of the diagonal of a square with side a units is 2a .

PRACTICE TIME

1. The length of a rectangle is 14 cm and its perimeter is equal to the perimeter of a square with side
12.5 cm. Find the area of the rectangle.

2. The perimeter of a trapezium is 65 cm and its non-parallel sides are 15 cm and 14 cm. If the height of
the trapezium is 24 cm, find its area.
3. A vehicle having a wheel with diameter 7 m covers a distance of 16,500 m. Find the number of revolutions
made by the wheel to cover the distance.
4. The diagonals of a rhombus are of length 16 cm and 24 cm. Find its area.
5. A parallelogram-shaped tile has a base of 28 cm and the corresponding altitude of 14 cm. How many
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such tiles are required to cover a floor with area 98 m ?
6. In the adjoining figure, ABC is a right-angled triangle and BDEF is a square. 10 cm
Find the length of each side of the square if AC = 26 cm and BC = 10 cm. C D B
(Hint: Area of square BDEF = Area of ∆ABC – Area of ∆AEF – Area of ∆DCE)
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7. The area of an annulus (ring) is 1,848 cm . Find the radii of the two circles if their 26 cm F
E
difference is 14 cm.
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8. A metallic wire is bent to form a square with an area of 484 cm . Find: A
(a) the length of the wire.

(b) the largest area enclosed, when the same wire is rebent to form a circle.

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