NCERT Solutions for Class 8 Maths Exercise 11.3

NCERT Solutions for Class 8 Maths Exercise 11.3 Class 8 Maths book solutions are available in PDF format for free download. These ncert book chapter wise questions and answers are very helpful for CBSE exam. CBSE recommends NCERT books and most of the questions in CBSE exam are asked from NCERT text books. Class 8 Maths chapter wise NCERT solution for Maths Book all the chapters can be downloaded from our website and myCBSEguide mobile app for free.

NCERT solutions for Class 8 Maths Mensuration Download as PDF

NCERT Solutions for Class 8 Maths Mensuration

Class –VIII Mathematics (Ex. 11.3)

NCERT SOLUTION

1. There are two cuboidal boxes as shown in the adjoining figure. Which box requires the lesser amount of material to make?

Ans. (a) Given: Length of cuboidal box  = 60 cm

Breadth of cuboidal box  = 40 cm

Height of cuboidal box  = 50 cm

 Total surface area of cuboidal box

= ]

= 2 (60  40 + 40  50 + 50 60)

= 2 (2400 + 2000 + 3000

= 2  7400 = 14800

(b) Given: Length of cuboidal box

= 50 cm

Breadth of cuboidal box  = 50 cm

Height of cuboidal box  = 50 cm

 Total surface area of cuboidal box

=

= 2 (50  50 + 50  50 + 50  50)

= 2 (2500 + 2500 + 2500)

= 2  7500 = 15000

Hence cuboidal box  requires the lesser amount of materal to make, since surface area of box  is less than that of box

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NCERT Solutions for Class 8 Maths Exercise 11.3

2. A suitcase with measures 80 cm  48 cm  24 cm is to be covered with a tarpaulin cloth. How many meters of tarpaulin of width 96 cm is required to cover 100 such suitcases?

Ans. Given: Length of suitcase box = 80 cm, Breadth of suitcase box  = 48 cm

And Height of cuboidal box  = 24 cm

 Total surface area of suitcase box

=

= 2 (80  48 + 48  24 + 24  80)

= 2 (3840 + 1152 + 1920)

= 2  6912 = 13824

Area of Tarpaulin cloth = Surface area of suitcase

  = 13824

 

  = 144 cm

Required tarpaulin for 100 suitcases

= 144  100 = 14400 cm = 144 m

Hence tarpaulin cloth required to cover 100 suitcases is 144 m.

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NCERT Solutions for Class 8 Maths Exercise 11.3

3. Find the side of a cube whose surface area id 600.

Ans. Here Surface area of cube = 600 cm²

  = 600

  = 100

  = 10 cm

Hence the side of cube is 10 cm

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4. Rukshar painted the outside of the cabinet of measure 1 m 2 m  1.5 m. How much surface area did she cover if she painted all except the bottom of the cabinet?

Ans. Here, Length of cabinet  = 2 m, Breadth of cabinet  = 1 m

And Height of cabinet  = 1.5 m

 Surface area of cabinet =

= 2  1 + 2 (1  1.5 + 1.5  2)

= 2 + 2 (1.5 + 3.0)

= 2 + 9.0

= 11

Hence required surface area of cabinet is 11.

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NCERT Solutions for Class 8 Maths Exercise 11.3

5. Daniel is paining the walls and ceiling of a cuboidal hall with length, breadth and height of 15 m, 10 m and 7 m respectively. From each can of paint 100 of area is painted. How many cans of paint will she need to paint the room?

Ans. Here, Length of wall  = 15 m, Breadth of wall  = 10 m

And Height of wall  = 7 m

 Total Surface area of classroom

=

= 15  10 + 2 (10  7 + 7 15)

= 150 + 2 (70 + 105)

= 150 + 350

= 500

Now Required number of cans

=  = 5 cans

Hence 5 cans are required to paint the room.

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NCERT Solutions for Class 8 Maths Exercise 11.3

6. Describe how the two figures below are alike and how they are different. Which box has larger lateral surface area?

Ans. Given: Diameter of cylinder = 7 cm

 Radius  of cylinder  =  cm

And Height of cylinder  = 7 cm

Lateral surface area of cylinder =

=

= 154 cm²

Now lateral surface area of cube

=  = 4  49 = 196

Hence the cube has larger lateral surface area.

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NCERT Solutions for Class 8 Maths Exercise 11.3

7. A closed cylindrical tank of radius 7 m and height 3 m is made from a sheet of metal. How much sheet of metal is required?

Ans. Given: Radius of cylindrical tank  = 7 m

Height of cylindrical tank  = 3 m

Total surface area of cylindrical tank

=

=

= 44  10 = 440

Hence 440  metal sheet is required.

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NCERT Solutions for Class 8 Maths Exercise 11.3

8. The lateral surface area of a hollow cylinder is 4224. It is cut along its height and formed a rectangular sheet of width 33 cm. Find the perimeter of rectangular sheet?

Ans. Given: Lateral surface area of hollow cylinder = 4224

And Height of hollow cylinder = 33 cm

Curved surface area of hollow cylinder =

 4224 =

  =  cm

Now Length of rectangular sheet =

  = 128 cm

Perimeter of rectangular sheet =

= 2 (128 + 33) = 2 x 161 = 322 cm

Hence perimeter of rectangular sheet is 322 cm.

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NCERT Solutions for Class 8 Maths Exercise 11.3

9. A road roller takes 750 complete revolutions to move once over to level a road. Find the area of the road if the diameter of a road roller is 84 cm and length 1 m.

 

Ans. Given: Diameter of road roller = 84 cm

 Radius of road roller

= 42 cm

Length of road roller  = 1 m = 100 cm

Curved surface area of road roller =  =  = 26400 cm²

 Area covered by road roller in 750 revolutions = 26400  750

= 1,98,00,000

= 1980 m² [ 1 = 10,000]

Hence the area of the road is 1980.

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NCERT Solutions for Class 8 Maths Exercise 11.3

10. A company packages its milk powder in cylindrical container whose base has a diameter of 14 cm and height 20 cm. Company places a label around the surface of the container (as shown in figure). If the label is placed 2 cm from top and bottom, what is the area of the label?

Ans. Given: Diameter of cylindrical container = 14 cm

 Radius of cylindrical container  = 7 cm

Height of cylindrical container = 20 cm

Height of the label = 20 – 2 – 2

= 16 cm

Curved surface area of label =

=  = 704 cm²

Hence the area of the label of 704 cm².

NCERT Solutions for Class 8 Maths Exercise 11.3

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