Speed of evaporation of tank

Question

I am given $a$ and $b$ and the program should return the speed of evaporation(in percentages), if I know that the fluid from a tank evaporates to $a\%$ from the starting amount of the fluid, in $b$ months.

Answer 1

HINT:

You have to define the law of evapouration.

Assuming a similar Newton's law of evaporative cooling.

$$ \dfrac{dy}{dt}=-k y \;, y=y_0 e^{-k t}$$

For given

$$y/y_0= 1-a/100, t= b$$

evaluate $k$ by taking logs.