Question

ALL AREA AND VOLUME OF A CUBOID AND A CUBE
18.15
A wooden bookshelf has external dimensions as follows: Height =
Nowe Height = 110 cm,
1
Depth = 25 cm, Breadth = 85 cm (See Fig. 18.5). The thickness of the plank is 5 cm
everywhere. The external faces are to be polished and the inner faces are to be painted.
If the rate of polishing is 20 paise per cm2 and the rate of painting is 10 paise per me
Find the total expenses required for polishing and painting the surface of the
bookshelf.
[NCERT)
85 cm
110 cm
25 cm​

Answer 1

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ANSWER

External length =85cm

External breadth =25cm

External height =110cm

External SA=lh+2(lb)+2bh

=85×110+2(85×25+25×110)

=(9350+9750)cm

2

=19100cm

2

Area to be polished =19100+2600=21700cm

2

Cost of polishing 1cm

2

area 0.20Rs

Cost of polishing 21700cm

2

area =21700×0.20

=Rs. 4340

Now, area to be painted in 3 rows =3× area to be painted in 1 row

=3×[2(l+b)b+lh]

=3[2(75+30)×20+30×75]

=3[4200+2250]=19350cm

2

Cost of painting 1 cm

2

area =0.10Rs

Cost of painting 19350 area =Rs.1935

Total cost =1935+4340

=Rs.6275

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