Question

If it costs Rs y to whitewash the 4 walls of a room, how much it would cost of all the
dimensions were to be 5 times more?
(a) Rs 5y
(6) Rs 25y
(c) Rs 25y²
(d) Rs 20y​

Answer 1

The cost to whitewash the 4 walls when all the  dimensions were to be 5 times more is Rs 25y

Solution:

Let’s first find the area of four walls of the room

Let’s length of the room = l , width of the room = w and height of the room = h

Let’s first find the area of four walls of the room

Let’s length of the room = l, width of the room = w and height of the room = h

So area of four walls = lh + wh + lh + wh = 2 ( lh + wh)  

So to white wash area of 2 ( lh + wh)  cost is Rs y

Now let’s increase dimension by 5 times

So new length = 5l, new width = 5 and new height = 5h

New increased area of four walls  = 5l x 5h + 5w x 5h +  5l x 5h + 5w x 5h  

= 25 ( lh + wh + lh + wh) = 25 x  2( lh + wh) = 25 x initial area

Since area get increased by 25 times after increasing the dimensions by 5 times , so cost will also increase 25 times that is cost will increase from y to 25y .

Hence correct option is b that is Rs 25 y