Aptitude - Area - Discussion

Thanks to all. Now it's easy to understand.

I wish to elaborate this further.

It is given that Tank is Long, Wide and Deep. It leads to assumption that Tank is Cuboid or Rectangular Prism.

It is not given that Cuboid is in shape of Rhombus or Parallelogram. Therefore, due to benefit of doubt, we assume it to be Rectangular Cuboid.

Following is diagram:-

__.
W |\__\ H.
\|__|.
L.

Length = 25 m.
Width = 12 m.
Height = 6 m.

There are total four walls. Area of four walls will not be equal, because Cuboid 's Length? Cuboid 's Width.

Therefore, 4*(Length*Height) is NOT possible.

Out of four walls, two walls lie opposite to each other with same dimensions. Therefore, its area will be equal.

Area of first two similar walls = 2*(Length*Height)....equation (1).

Remaining two walls will lie opposite to each other with same dimensions. Therefore, its area will be equal to each other, but different to equation (1).

Area of other two similar walls = 2*(Width*Height)....equation (2).

From equation (1) and equation (2),

Following will be true:-

Area of four walls = 2*(Length*Height)+2*(Width*Height).

= 2*Height*(Length+Width).
= 2*6*(25+12).
= 2*6*37.
= 444 sq.m.

Area of Bottom.

= Length*Width.
= 25 x 12.
= 300 sq.m.

Area of Walls and Bottom = 444+300 = 744 sq.m.

=> Cost of plastering = 744 sq.m. x Rs. 0.75 = Rs.558.

Why (l x b) is there again?

How do you know the tank is of rectangular shape, since it is not mentioned in the question. It can be of any other shape. What is the reason behind assuming it a rectangular shape.

Area of 4 walls of a room = 2 (Length + Breadth) x Height.(Standard Formula).

Here, 2(l+b)*h for four walls, and the bottom is extra.

So here we add the area of bottom.

[2(l+b)*h]*(l*b)...

I guess This will help!!

What is the formula if it is a room and need to plaster four walls, bottom and top as well ?

How you know the bottom is rectangular or may be any other?

@malar

2(l+b) is only the perimeter of the rectangle (2D) with only length and breadth and no thickness / depth.

Here it is the wall of the tank with depth of 6 m.

Hope you got the idea.

Formula for four walls is 2(l+b)*h so we have to multiply by h this is for four walls but here it is given as tank so v huv to cover the bottom area also so (l*b).

Hence to find we have to add both 2(l+b)h +(l*b).

For walls its enough [2(l+b)] . Then why you multiply with h ?