Question

The length, breadth and height of a room are in the ratio 7:3:1. If the breadth and height are doubled while the length is halved, then by what percent the total area of the 4 walls of the room will be increased ?
A) 90%
B) 88%
C) 85%
D) 84%

Answer 1

Q:

The length, breadth and height of a room are in the ratio 7:3:1. If the breadth and height are doubled while the length is halved, then by what percent the total area of the 4 walls of the room will be increased  ?

A) 90%
B) 88%
C) 85%
D) 84%

Answer:   A) 90% 

Explanation:

Let length, breadth and height of the room be 7, 3, 1 unit respectively.
Area of walls = 2(l+b)xh = 2(7+3)x1 = 20 sq. unit.
Now, length, breadth and height of room will become 3.5, 6 and 2 respectively. 
Area of walls = 2(l+b)xh = 2(3.5+6)x2 = 38 sq. unit. 
% Increase in the area of walls =
(38-20)x100/20 = 90%.