How are probabilities calculated in games?

Question

PHP

Let's say there is an 80% chance that it will rain today.
In what way in games do they calculate whether he will go?
And is this simple method fair:
ver = random(1, 100);
If ver > 80 then it won't work, if ver<80 then it will. Or does it look like crap?

Answer 1

add a few conditions
not just by chance, but also by checking for the time since the last rain. so that it often was not and was not for a long time

Answer 2

Not nonsense. That's pretty much what happens.
From the word Korean random.

Answer 3

Yes, they do. Only usually operate with numbers less than 1.
raining = random() < 0.8