Page 9 - Lesson Notes-Ch.13 SA and Volumes(Cuboids and Cubes)

Total surface area of the cereal box = 2(lb + bh + lh)
= 2(80 × 40 + 40× 20 + 20 × 80)
= 2(3200 + 800 + 1600)
2
= 2(5600) = 11200 cm
Area of Sheet of each square paper = ( ) = ×
2
=(40× 40) = 1600
2
2
ℎ
So, No. of Sheets required =
ℎ

11200
= = 7
1600
Example -6:
Hameed has built a cubical water tank with lid for his house, with each
outer edge 1.5 m long. He gets the outer surface of the tank excluding
the base, covered with square tiles of side25 cm. Find how much he
would spend for the tiles, if the cost of the tiles is Rs.360 per dozen?
Solution

Given, Edge of the cubical tank = 1.5 m = 150 cm (= )
2
Total surface area of the tank to be covered with tiles = 5 [Excluding base]
2
= (5× 150 × 150) cm
2
Area of Sheet of each square tile = ( ) = ×
=(25× 25)
2
ℎ
So, No. of tiles required =

5×150×150
= = 180
25×25
Cost of one dozen tile (i.e. 12 tiles) = Rs. 360
360
Cost of one tile = = Rs. 30
12
So, total cost of 180 tiles = . (180× 30) = Rs. 5400
Example -7:
Find the perimeter of the cuboid whose length 12 cm, breadth 8 cm and
height 3 cm.
Solution:
Given,
Length(l) = 12 cm Breadth(b) = 8 cm Height(h) = 3 cm
Perimeter of the cuboid = 4(l + b +h)
= 4(12 + 8 + 3) cm =92 cm
Example -8:
Find the perimeter of the cube whose each equal side is 5 cm.
Solution:
Given, Side of the cube ( )= 5 cm
So, Perimeter of the cube = 12 = (12× 5) cm = 60 cm.
Example-9

Find the volume of a cuboid of dimensions 14 cm × 12 cm × 8 cm.

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