Bunuel wrote:

earnit wrote:

I am unable to understand the logic behind 30/(area/2).

As per my understanding, There are two circular bases of a cylinder since we are looking at one (from where water evaporates) so Area/2.

Combining these entities ALL together seems like a problem here.

Concepts that involve three dependent quantities tend to be always tricky like 2 litre PER hour PER one square meter of surface.

How to get a hang of such questions?

There was a formatting error. Edited.

Water evaporates from the top of a pool, which is open. We are told that

2 liters evaporate from each square meter of surface per 1 hour.

So, to find the time needed for 30 liters of water to evaporate we need to find the surface area of the top of the cylinder: \(2*area\) will be the amount of water that evaporates each hour, thus \(time=\frac{30}{2*area}\).

For example if the surface area of the top is 5m^2, then in one hour 5*2=10 liters of water evaporates hence it'll take 30/10=3 hours 30 liters of water to evaporate.

So as per my understanding i will further elaborate the explanation.

The key takeaway from this Question is managing three dependent entities, taking two at a time.

2 liters evaporate

from each square meter (PER square meter) of surface PER hour.

One look at it seems like a three way battle but here's how it was broken down.

Quantity that Evaporate ----

Surface Area (top) 2 Liters ---- 1 m^2

? ---- Surface Area of Cylinder (top)

So, 2*Surface Area of Cylinder = 2*area is the quantity that evaporates in 1 hour.

Now, 2* area is the quantity that evaporates in 1 hour

so, 30 liters will take =[

30/(2*area)] hours

Hence, a connecting flow from Quantity to Area to finally time.