Rule of three units
The principle is quite simple: You need to do the same on both sides to achieve the desired result.
* unity of place (a) - taking place of the event in only one place
* unity of time (b) - the event must take place within 24 hours
* plot unity (c) - simple line, as few turns as possible

Straightforward rule of three
If one quantity is greater, the other increases in the same proportion.
a/b = c/d
It is possible to calculate a, b and c. To calculate d:
d = c * b / a

The inverse rule of three
In the same ratio, if one quantity is greater, the other will decrease.
It is possible to calculate d using the following formulas: a, b and c. To calculate d:
d = a*b/c

DEUS EX MACHINA