If an event attempts to get past fortune tellers, then 20 fortune tellers with 5% will have ~64% of stopping that event.
The formula goes: 1-(1-P)^n, P is the probability of stopping an event (0.05 in this case), and n is the number of fortune tellers (20 in this case).
Explanation: The chance for a fortune teller to prevent the event is P, so the chance of the event getting past that fortune teller is (1-P), so the chance for getting past all of the fortune tellers is (1-P)^n, so if we want to see what the chance of the event not getting past all of the fortune tellers we get 1-(1-P)^n.
(Feel free to correct me if I'm mistaken
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