Question

the lenght,breadth and height of a room are 5m,4m and 3.5m respectively. Find the area of four walls of the room leaving aside 3 windows each of dimensions 2m by 1m and 2 doors each of dimensions 2m by 1.5m.

Answer 1

length of room is l = 5m
breath of room is b = 4m
height of room is h = 3.5m

3 windows each of dimensions 2m by 1m
so area of window = 2*1 = 2m²
so area of 3 windows is 3*2 = 6m²

2 doors each of dimensions 2m by 1.5m
so area of door = 2*1.5 = 3m²
so area of 2 door is 2*3 = 6m²

area of 2 walls of length of 5m by height of 3.5m = 2(5*3.5) = 2(17.5) = 35m²

area of another 2 walls of breath of 4m by height of 3.5 m = 2(4*3.5) = 2(14) = 28m²

area of four walls = 35+28 = 63m²

area of four walls excluding 3 windows and 2 doors = 63 - 6 - 6 = 63 - 12 = 51m²

Answer 2

Area of four walls = Base perimeter x Height 
= 2(l + b)h 
= 2(5 + 4)3.5
= 2 x 9 x 3.5 = 18 x 3.5 = 63 m². 

Area of 3 windows
= (2 x 1)3 = 2 x 3 = 6 m². 

Area of 2 doors 
= (2 x 1.5)2 = 3 x 2 = 6 m². 

Area of four walls excluding doors and windows
= 63 - (6 + 6) = 63 - 12 = 51 m². 

51 m² is the answer.