Aptitude - Volume and Surface Area - Discussion

Total Surface[2(lb + lh + bh)] - (upper most surface of water)[lb]
tis concept is clear bcoz water is not touching surface of tank
but i m not getting why 2(bh + lh) + lb this step is used.. specialy (+ lb)

Because it is not full till the top

The question is about wet surface area, then why do they subtract the lb. ?or they are asking about the wall surface alone.

Its because the other side (top surface) won't get wet.

Otherwise use 2*6*1.25+2*4*1.25+6*4= 49.

Is it a cuboid ..? because 2(lb+bh+lh) is the formulae of a surface area of cuboid. I didnt get why are we subtracting lb from it ? Can anyone help me out with an pictorial diagram ?

Just imagine that the cuboid is full but the upper surface was empty

So we have to minus that part and take the l=6,b=4,h=1.25

I think now you got it.

Why cuboid? is it not a cylinder?

Because all the answers are in "meter square". If its cylinder then it will be in meter cube.

Let me explain.

Consider a water tank with half of the water .
Now the inner surface of the water tank will get wet but not the of waster(upper most surface of water on which things float)
So we need to deduct that part (area of that part) from total surface of Cuboid
hence .

Total Surface[2(lb + lh + bh)] - (upper most surface of water)[lb]

@Fainaz : when we calculate area the unit is "met Sqr" nad when we calculate Volume the unit is "met cube". It has noyhing to do with Cuboid or Cylinder.

@Roshan : we need to consider it Cuboid bcoz they have written "6m long and 4 m". if It is Cylinder , they might have given diameter ... got it ;)