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#### Chapters

1 - Number Systems2 - Polynomials

3 - Coordinate Geometry

4 - Linear Equations in two Variables

5 - Introduction to Euclid's Geometry

6 - Lines and Angles

7 - Triangles

8 - Quadrilaterals

9 - Areas of Parallelograms and Triangles

10 - Circles

11 - Constructions

12 - Heron's Formula

13 - Surface Area and Volumes

14 - Statistics

15 - Probability

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### Chapter 12 - Heron's Formula

#### Pages 202 - 203

A traffic signal board, indicating ‘SCHOOL AHEAD’, is an equilateral triangle with side ‘*a*’. Find the area of the signal board, using Heron’s formula. If its perimeter is 180 cm, what will be the area of the signal board?

The triangular side walls of a flyover have been used for advertisements. The sides of the walls are 122m, 22m, and 120m (see the given figure). The advertisements yield an earning of Rs 5000 per m^{2}per year. A company hired one of its walls for 3 months. How much rent did it pay?

There is a slide in the park. One of its side walls has been painted in the same colour with a message “KEEP THE PARK GREEN AND CLEAN” (see the given figure). If the sides of the wall are 15m, 11m, and 6m, find the area painted in colour.

Find the area of a triangle two sides of which are 18 cm and 10 cm and the perimeter is 42 cm.

Sides of a triangle are in the ratio of 12: 17: 25 and its perimeter is 540 cm. Find its area.

An isosceles triangle has perimeter 30 cm and each of the equal sides is 12 cm. Find the area of the triangle.

#### Pages 206 - 207

A park, in the shape of a quadrilateral ABCD, has ∠C = 90°, AB = 9 m, BC = 12 m, CD = 5 m and AD = 8 m. How much area does it occupy?

Find the area of a quadrilateral ABCD in which AB = 3 cm, BC = 4 cm, CD = 4 cm, DA = 5 cm and AC = 5 cm.

Radha made a picture of an aeroplane with coloured papers as shown in the given figure. Find the total area of the paper used.

A triangle and a parallelogram have the same base and the same area. If the sides of triangle are 26 cm, 28 cm and 30 cm, and the parallelogram stands on the base 28 cm, find the height of the parallelogram.

A rhombus shaped field has green grass for 18 cows to graze. If each side of the rhombus is 30 m and its longer diagonal is 48 m, how much area of grass field will each cow be getting?

An umbrella is made by stitching 10 triangular pieces of cloth of two different colours (see the given figure), each piece measuring 20 cm, 50 cm and 50 cm. How much cloth of each colour is required for the umbrella?

A floral design on a floor is made up of 16 tiles which are triangular, the sides of the triangle being 9 cm, 28 cm and 35 cm (see the given figure). Find the cost of polishing the tiles at the rate of 50p per cm^{2}.

A kite in the shape of a square with a diagonal 32 cm and an isosceles triangles of base 8 cm and sides 6 cm each is to be made of three different shades as shown in the given figure. How much paper of each shade has been used in it?

A field is in the shape of a trapezium whose parallel sides are 25 m and 10 m. The non-parallel sides are 14 m and 13 m. Find the area of the field.

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