If the length, breadth and height of the room are in the ratio 3:2:1. The breadth and height of the room are halved and length of the room is doubled. Then area of the four walls of the room will,
Let length be 3x ,breadth be 2x and height be x
Now we know that the area of four walls = 2h(l+b) = 2x(5x) = 10x^2
Now new length = 6x , new height = 0.5x and new breadth = x
So the area of four walls will now be : 2(0.5x)(7x)= 7x^2
Now therefore percentage change in area : $$\frac{7x^2-10x^2}{10x^2}\times\ 100\ =\ 30\%$$
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