How do i execute one event in php based on a probability for the event to happen
Use rand():
if (rand(1,100)<=$chance)This will return a number between 1 and 100, so that the probability of it being lower or equal to 40 is 40%.
Umm... Either I'm losing it or you mean you want the below...
$chance = 40;if ($chance >= 40){ echo "event happened"; //do the event} else { echo "event didn't happened";}This assumes that the chance is equal to or is more than 40.
If you want chance to be randomly generated, then use something like $chance = rand(0,100); for a random number between 0 and 100 - then just use if statements to do the conditions.
At the end of the day it depends if your initial $chance is a fixed number or it is random or occurs as a result of a calculation.... unfortunately you haven't provided much insight...