> if the baseline chance of delay is 10%, engineering works add 25%, strikes add 35%, and bad weather adds 20%, then when all these problems happen, there's a 90% chance your train will be delayed. What if signal failures "add" 15%? Then all factors combined would mean that there's a 105% chance your train will be delayed! Adding up probabilities like this doesn't make sense. If you simplify these things as independe…
>>> s = 'if the baseline chance of delay is 10%, engineering works add 25%, strikes add 35%, and bad weather adds 20%'
>>> pb = 0.1
>>> pe = 0.25
>>> ps = 0.35
>>> pw = 0.2
>>> p = 1 - (1 - pb)*(1 - pe)*(1 - ps)*(1 - pw)
>>> p
0.649