RD Sharma - Mathematics

Book: RD Sharma - Mathematics

Chapter: 21. Mensuration-II (Volumes and Surface Areas of a Cuboid and a Cube)

Subject: Maths - Class 8th

Q. No. 16 of Exercise 21.3

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16

A classroom is 7 m long, 6 m broad and 3.5 m high. Doors and windows occupy an area of 17 m2. What is the cost of white washing the walls at the rate of Rs. 1.50 per m2.

Given,


Dimensions of class room = 7m × 6m ×3.5m


Where,


Length = 7m, Breadth = 6m , Height = 3.5 m


Area of four walls (including doors & windows) =


=


Then,


Area of walls without doors & windows =


= area including doors & windows – area occupied by doors & windows


Area of only walls = 91 – 17 = 74 m2


So,


Cost of white washing 1 m2 area of walls = Rs.1.50


∴ Total cost of white washing = 74 × 1.50 = Rs.111


16

Chapter Exercises

Exercise 21.1
Exercise 21.2
Exercise 21.3
Exercise 21.4

More Exercise Questions

1

Find the surface area of a cuboid whose

(i) length = 10 cm, breadth = 12 cm, height = 14 cm


(ii) length = 6 dm, breadth = 8 dm, height = 10 dm


(iii) length = 2m, breadth = 4 m, height = 5 m


(iv) length = 3.2 m, breadth = 30 dm, height = 250 cm.
2

Find the surface area of a cube whose edge is

(i) 1.2 m


(ii) 27 cm


(iii) 3 cm


(iv) 6 m


(v) 2.1 m
3

A cuboidal box is 5 cm by 5 cm by 4 cm. Find its surface area.
4

Find the surface area of a cube whose volume is

(i) 343 m3


(ii) 216 dm3
5

Find the volume of a cube whose surface area is

(i) 96 cm2


(ii) 150 m2
6

The dimensions of a cuboid are in the ratio 5 : 3 : 1 and its total surface area is 414 m2. Find the dimensions.
7

Find the area of the cardboard required to make a closed box of length 25 cm, 0.5 m and height 15 cm.
8

Find the surface area of a wooden box whose shape is of a cube, and if the edge of the box is 12 cm.
9

The dimensions of an oil tin are 26 cm× 26 cm× 45 cm. Find the area of the tin sheet required for making 20 such tins. If 1 square metre of the tin sheet costs Rs. 10, find the cost of tin sheet used for these 20 tins.
10

A classroom is 11 m long, 8 m wide and 5 m high. Find the sum of the areas of its floor and the four walls (including doors, windows etc.)
11

A swimming pool is 20 m long 15 m wide and 3 m deep. Find the cost of repairing the floor and wall at the rate of Rs. 25 per square metre.
12

The perimeter of a floor of a room is 30 m and its height is 3 m. Find the area of four walls of the room.
13

Show that the product of the areas of the floor and two adjacent walls of a cuboid is the square of its volume.
14

The walls and ceiling of a room are to be plastered. The length, breadth nad height of the room are 4.5 m, 3 m and 350 cm, respectively. Find the cost of plastering at the rate of Rs. 8 per square metre.
15

A cuboid has total surface area of 50 m2 and lateral surface area os 30 m2. Find the area of its base.
16

A classroom is 7 m long, 6 m broad and 3.5 m high. Doors and windows occupy an area of 17 m2. What is the cost of white washing the walls at the rate of Rs. 1.50 per m2.
17

The central hall of a school is 80 m long and 8 m high. It has 10 doors each of size 3 m ×1.5 m and 10 windows each of size 1.5 m× 1 m. If the cost od white washing the walls of the hall at the rate of Rs. 1.20 per m2 is Rs. 2385.60, find the breadth of the hall.