Page 239 - Start Up Mathematics_7

8. Complete the following table:

Figure Length Breadth Area Perimeter
Square 169 cm 2
Rectangle 80 cm 8 m
Square 4.84 m
9. The area of a rectangle is same as that of a square of side 16 m. If the length of the
rectangle is 32 m, find its perimeter.

10. Barbed wire is to be put around a rectangular flowerbed measuring 20 m by 12 m. If poles
are erected after every one metre so that the barbed wire can be put around it, how many
poles will be needed in all?

Maths Lab Activity
I: Area of a parallelogram

A D

Step 1: Draw a parallelogram ABCD on a sheet of coloured
paper and cut it using a pair of scissors.
B C
A D

Step 2: Draw a perpendicular from vertex A to meet BC II
at E. Let the perpendicular divide the figure into I Altitude
two regions I and II.
B E Base C

Step 3: Cut the parallelogram along the altitude to separate regions I and II. Paste regions
I and II in the interchanged positions to form a rectangle as shown.

A′ A″ D A″ D A′ A″ D(A′)

I II II I

B E′ E″ C E″ C B E′ E″ C(B) E′

Thus, area of parallelogram = Area of rectangle
= length × breadth Altitude
(breadth)
= base × altitude

Base (length)
II: Area of a triangle A
Step 1: Draw a triangle ABC on a white sheet of paper.

B C

231