A wooden bookshelf has external dimensions asfollows: Height 110 cm, D

1.	A wooden bookshelf has external dimensions asfollows: Height 110 cm, Depth 25 cm,Breadth 85 cm (see Fig. 13.31). The thickness ofthe plankare to be polished and the inner faces are to bepainted. If the rate of polishing is 20 paise percm2 and the rate of painting is 10 paise per emfind the total expenses required for polishing andis 5 cm everywhere. The external faces2inting the surface of the bookshelf.
Answer» External faces to be polished = Area of six faces of cuboidal bookshelf – 3 (Area of open portion ABCD) = 2 (110 x 25 + 25 x 85 + 85 x 110) – 3 (75 x 30) [AB = 85 – 5 – 5 = 75 cm and AD =x 110 – 5 – 5 – 5 – 5 = 30 cm] = 2 (2750 + 2125 + 9350) – 3 x 2250 = 2 x 14225 – 6750 = 28450 – 6750 = 21700 cm2 Now, cost of painting outer faces of wodden bookshelf at the rate of 20 paise. = Rs. 0.20 per cm2= Rs. 0.20 x 21700 = Rs. 4340 Here, three equal five sides inner faces. Therefore total surface area = 3 [ 2 (30 + 75) 20 + 30 x 75] [Therefore, Depth = 25 – 5 = 20 cm] = 3 [ 2 x 105 x 20 + 2250] = 3 [ 4200 + 2250] = 3 x 6450 = 19350 cm2 Now, cost of painting inner faces at the rate of 10 paise i.e. Rs. 0.10 per cm2. = Rs. 0.10 x 19350 = Rs. 1935 Total expenses required = Rs. 4340 + Rs. 1935 = Rs. 6275

A wooden bookshelf has external dimensions asfollows: Height 110 cm, Depth 25 cm,Breadth 85 cm (see Fig. 13.31). The thickness ofthe plankare to be polished and the inner faces are to bepainted. If the rate of polishing is 20 paise percm2 and the rate of painting is 10 paise per emfind the total expenses required for polishing andis 5 cm everywhere. The external faces2inting the surface of the bookshelf.

Answer»

External faces to be polished

= Area of six faces of cuboidal bookshelf – 3 (Area of open portion ABCD)

= 2 (110 x 25 + 25 x 85 + 85 x 110) – 3 (75 x 30)

[AB = 85 – 5 – 5 = 75 cm and AD

=x 110 – 5 – 5 – 5 – 5 = 30 cm]

= 2 (2750 + 2125 + 9350) – 3 x 2250

= 2 x 14225 – 6750

= 28450 – 6750

= 21700 cm2

Now, cost of painting outer faces of wodden bookshelf at the rate of 20 paise.

= Rs. 0.20 per cm2= Rs. 0.20 x 21700 = Rs. 4340

Here, three equal five sides inner faces.

Therefore total surface area

= 3 [ 2 (30 + 75) 20 + 30 x 75]

[Therefore, Depth = 25 – 5 = 20 cm]

= 3 [ 2 x 105 x 20 + 2250] = 3

[ 4200 + 2250]

= 3 x 6450 = 19350 cm2

Now, cost of painting inner faces at the rate of 10 paise i.e. Rs. 0.10 per cm2.