Question

85 cm
25 cm,
A wooden bookshelf has external dimensions as
follows: Height 110 cm, Depth
Breadth=85 cm (see Fig. 13.31). 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 cm”,
find the total expenses required for polishing and
painting the surface of the bookshelf.
110
25 cm

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Answer 1

$\huge\bold\red{Question:}$

A wooden bookshelf has external dimensions as follows : Height = 110 cm, 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 cm². Find the total expenses required for polishing and painting the surface of the bookshelf.

$\huge\bold\green{Solution:}$

External length $(l)$ of bookshelf=$85cm$

External breadth $(b)$ of bookshelf=$25cm$

External height $(h)$ of bookshelf=$110cm$

External surface area of book shelf while leaving out the front face of the shelf

=$lh+2(lb+bh)$

=$(85×110)+2(85×25+25×110)$

=$9350+9750$

=$19100cm^2$

Area of front face

=$(85×110)−75×100+2(75×5)$

=$1850+760=2600cm^2$

Area to be polished

=$19100+2600$

=$21700cm^2$

Cost of polishing

= $₹\:21700×0.20$

= $₹4340$

Length, breadth and height of each row of bookshelf are

$75cm,20cm\: and \:30 cm.$

From the figure Area to be painted in 1 row

=$2(l+h)b+lh$

=$2(75+30)20+75×30$

=$6450cm^2$

Area to be painted in 3 rows

= $3×6450=19350cm^2$

Total cost of painting

=$₹(19350×0.1)=₹ 1935$

Total expenses

=$₹(4340+1935)=₹\:6275$

Answer 2

Answer:

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