Question

A room is 20m long, 15m wide and 12m high. It contains a door 7.5m × 4m and two windows of size 4m × 2.5m. Find the cost of painting its wall @ rs. 15 per m2​

Answer 1

Answer:

Total surface area of the room=2(lh+lb+hb)m

2

=2[9×6.5+9×8+8×6.5]m

2

=365m

2

Area of the door =l×b=2×1.5=3m

2

Area of the windows=l×b=1.5×1=1.5m

2

∴ Surface area of walls=TSA of room −Area of door−Area of windows

=365−3−1.5=360.5m

2

Cost of whitewashing per square meter=Rs. 6.40

∴ Cost of whitewashing the walls=Rs. 6.40×360.5

=Rs. 2307.2.

Answer 2

Length of room = 20 m

breath of room = 15 m

height of room = 12 m

$\sf \: Total \: S.A = 2(lb + bh + hl) \\ \sf \implies \: 2(20 \times 15 + 15 \times 12 + 12 \times 20) \\ \sf \implies \: 2(300 + 180 + 240) \\ \sf \implies \: 2(720) \\ \sf \implies \: 1440 \: {m}^{2}$

$\sf \implies \: Area \: of \: door \: = \: l \times b \\ \sf \: = \: 7.5 \times 4 \\ \sf \: = \: 30 \: {m}^{2}$

$\sf \implies \: Area \: of \: two \: windows \: = \: 2(4 \times 2.5) \\ \sf = \: 2(10) \\ \sf \: = \: 20 \: {m}^{2}$

$\sf \: Surface \: area \: of \: its \: walls = Total \: S.A - Area \: of \: door - Area \: of \: windows$

$\sf \: = \: 1440 {m}^{2} - 20 {m}^{2} - 10 {m}^{2} \\ \sf \: = 1410 {m}^{2}$

$\sf \implies \: Cost = rs. \: 15 × 1410 \: \\ \boxed{ \red{\sf{ = rs. \: 24150}}}$