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Q10.    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 the figure). If the label is placed 2 cm from top and bottom, what is the area of the label.

        

Area of label =  2πrh                       Here height is found out as = 20-2-2 = 16 cm. 

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 is 1 m.

        

 

Area in one complete revolution of roller =  2πrh.                                                                 So area of road  

8.  The lateral surface area of a hollow cylinder is 4224 cm^{2}. It is cut along its height and formed a rectangular sheet of width 33 cm. Find the perimeter of rectangular sheet?

Lenght of rectangular sheet                                                So perimeter of rectangular sheet = 2(l + b)                                                       . Thus perimeter of rectangular sheet is 322 cm.

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?

Total surface area of cylinder = 2πr (h + r)                                               

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

        

The two figures have same height.The diference between them is one is cylinder and another is cube. lateral surface area of cylinder =                                                                                                        lateral surface area of cube =                                                                                                                                ...

Daniel is painting 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 m^{2} of area is painted. How many cans of paint will she need to paint the room?

        

Total area painted by Daniel :                                                                                          (  Bottom surface is excluded.) So,  Area                                                  No. of cans of paint required                                                       Thus 5 cans of paint are required.

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

        

Required area = Total area - Area of bottom surface Total area     Area of bottom surface   So required area = 

Find the side of a cube whose surface area is 600 cm^{2}.

Surface area of cube    So,                        or                            or                           . Thus side of cube is 10 cm.  

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

Surface area of suitcase    . Area of such 100 suitcase will be  So lenght of tarpaulin cloth   

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

Surface area of cuboid (a)    Surface area of cube (b)    So box (a) requires the lesser amount of material to make.
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