The length, breadth and height of a room are in ratio 3:2:1. If breadth and height are halved while the length is doubled, then the total area of the four walls of the room will

Answer: Option E

Let length, breadth and height of the room be 3, 2, 1 unit respectively.
Area of walls = 2(l + b) × h = 2(3 + 2) × 1 = 10 sq. unit.
Now, length, breadth and height of room will become 6, 1 and $$\frac{1}{2}$$ respectively.
Now, area of walls = $$2\left(6+1\right)\times \frac{1}{2}$$   = 7 sq. unit.
% decrease in the area of walls = $$\left(10-7\right)\times \frac{100}{10}$$   = 30%