Question

The cost of white washing the four walls of a room is $Rs.25$. The cost of white washing a room twice in length, breadth and height will be:

• A. $Rs.50$
• B. $Rs.75$
• C. $Rs.100$
• D. $Rs.200$

Answer 1

The correct option is C $Rs.100$

Two walls will have the dimensions as length and height. Other two walls will have the dimensions as breadth, and height.
Hence, area of the four walls of the room $=2(l\times h)+2(b\times h)$
When length, breadth and height are doubled,
New Area $=2(2l\times 2h)+2(2b\times 2h)=4\times \left(2\right(l\times h)+2(b\times h\left)\right)=4\times OriginalArea$
When the area increases 4 times, the cost also becomes 4 times.
Hence, Cost of white washing the four walls of a room $=4\times Rs25=Rs100$