Page 196 - Start Up Mathematics_6

Problems Related to Observation Skills

Perimeter of Polygons
Find the perimeter of the following figures represented by A, B, C, D and E. Assume each
side of the square grid to be 1 unit. Record your observation in the given table. Discuss your
answer in the class.

Figure A B C D E
Perimeter (units)

C

D

A

B E

Example 1: Find the perimeter of each of the following figures:
5 cm 5 cm
20 cm 18 cm
7 cm

3 cm 6 cm 30 cm 30 cm 18 cm 18 cm 5 cm 5 cm

5 cm 40 cm 18 cm 5 cm 5 cm
(a) (b) (c) (d)

Solution: To find the perimeter of each of the above figures, we add the measure of all the
sides (clockwise or anticlockwise as per convenience):
(i) Perimeter of Fig. (a) = (7 + 6 + 5 + 3) cm = 21 cm

(ii) Perimeter of Fig. (b) = (20 + 30 + 40 + 30) cm = 120 cm

(iii) Perimeter of Fig. (c) = (18 + 18 + 18 + 18) cm = 72 cm
(iv) Perimeter of Fig. (d) = (5 + 5 + 5 + 5 + 5 + 5) cm = 30 cm

Example 2: The lid of a rectangular box of sides 30 cm by 10 cm is sealed all round with a tape.
What is the length of the tape required?
Solution: Length of the lid = 30 cm

Breadth of the lid = 10 cm
Length of the tape required = Perimeter of the lid

= 2(Length + Breadth)

= 2(30 + 10) cm = 80 cm

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