Question

A class-room is 12 m long, 10 m wide and 1.5 m.It has three windows each 1.5×0.5m and two doors each 2m long 1m.find the cost of painting its four walls at rupees ₹12 per square meter.

Answer 1

Length of room = 12 m

Breadth of room = 10 m

Height of room = 1.5 m

Room is cuboid in shape. So,

Curved surface area of cuboid = 2h(l + b)

Substitute the known values in above formula

=> 2 × 1.5(12 + 10)

=> 3(22)

=> 66 m²

Now,

Length of window = 1.5 m

Breadth of window = 0.5 m

So,

Area of 3 windows = 3(l + b)

Substitute the known values in above formula

=> 3(1.5 + 0.5)

=> 3(2)

=> 6 m²

Also,

Length of door = 2 m

Breadth of door = 1 m

Area of 2 doors = 2(l + b)

=> 2(2 + 1)

=> 2(3)

=> 6 m²

Area of four walls without doors and windows = CSA of room - (Area of 3 windows + Area of 2 doors)

=> 66 - (6 + 6)

=> 66 - 12

=> 54 m²

Cost of painting the four walls at Rs. 12 per m²

=> 54 × 12

=> Rs. 648

Answer 2

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Given question:-

A class-room is 12 m long, 10 m wide and 1.5 m.It has three windows each 1.5×0.5m and two doors each 2m long 1m.

To Find:-

find the cost of painting its four walls at rupees ₹12 per square meter.

Given:-

• 12m is the length of room
• 10m is the Breadth of room
• 1.5m is the height of room

2h(L × B) = curved surface area of cuboid.

Adding values:-

$= 2 \times 1.5(12 + 10) \\ = 3(22) = 66m {}^{2} \\ = 1.5 = window \: length \: \\ = 0.5 = window \: breadth$

3 (L × B) = area of three windows

Adding values:-

$= 3(1.5 + 0.5) \\ = 3(2) = 6m {}^{2}$

Hence,

$2m = door \: length \\ 1m = door \: breadth$

2 (L × B) = area of two doors.

$= (2 + 1) \\ = 2(3) = 6m {}^{2}$

Hence,

$= 66 - (6 + 6) \\ = 66 - 12 \\ = 54m {}^{2}$

Hence, 12 m² = Cost of painting the 4 walls.

$= 54 \times 12 \\ = 648$

Therefore, 648 is the cost of painting its four walls at rupees ₹12 per square meter.