Question

what would be the cost of putting a wire around each of these shapes given that 1cm wire costs 15​​

Answer 1

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Perimeter and Area- This chapter gives all the details about the perimeter and area of plane figures. Firstly the chapter discusses squares and rectangles.

Perimeter is the distance around a closed figure whereas area is the part of the plane occupied by the closed figure.

The perimeter of the following geometrical shapes are discussed in the first section:

Square

Perimeter of a square = 4 × side

Rectangle

Perimeter of a rectangle = 2 × (length + breadth)

The section is divided into two sub-parts:

1. Triangles as parts of rectangles

2. Generalising for other congruent parts of rectangles

Before moving onto exercise 11.2, the topics Area of triangle and parallelogram are discussed.

Area of a square = side × side

Area of a rectangle = length × breadth

Area of a parallelogram = base × height

Area of a triangle =1/2 × base × height

In the other half of the chapter, circles are explained. The topic is explained in two parts:

1. Circumference of Circle

The distance around a circular region is known as its circumference.

Circumference of a circle = πd

2. Area of circle

Area of circle is given by πr2

The last part of the chapter is about the conversion of units and application of the formulas.

Based on the conversion of units for lengths, studied in the chapter, the units of areas can also be converted:

1 cm2 = 100 mm2

1 m2 = 10000 cm2

1 hectare = 10000 m2

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Answer 2

Answer:

Length of the rectangular piece of land = 0.7 km = 0.7 x 1000 m = 700 m

Breadth of the rectangular piece of land = 0.5 km = 0.5 x 1000 m = 500 m

∴ Perimeter of the rectangular land

= 2 [length + breadth]

= 2 [700 m + 500 m]

= 2400 m.

Length of wire needed in 4 rounds of the land = 4 x 2400 = 9600 m = 9.6 km.