For safety reasons, four different alarm systems were installed in the vault containing the safety deposit boxes at a Beverly Hills bank. Each of the four systems detects theft with a probability of 0.99 independently of the others.The bank, obviously, is interested in the probability that when a theft occurs, at least one of the four systems will detect it.What is the probability that when a theft occurs, at least one of the four systems will detect it? (0.99)4 (0.01)4 1 − (0.99)4 1 − (0.01)4
Question
For safety reasons, four different alarm systems were installed in the vault containing the safety deposit boxes at a Beverly Hills bank. Each of the four systems detects theft with a probability of 0.99 independently of the others.The bank, obviously, is interested in the probability that when a theft occurs, at least one of the four systems will detect it.What is the probability that when a theft occurs, at least one of the four systems will detect it? (0.99)4 (0.01)4 1 − (0.99)4 1 − (0.01)4
Solution
The question is asking for the probability that at least one of the four alarm systems will detect a theft.
The easiest way to approach this problem is to calculate the probability that none of the systems detect the theft, and then subtract that from 1.
Each system independently has a 0.01 probability of not detecting a theft (1 - 0.99). Since the systems are independent, we can multiply these probabilities together to find the probability that all four systems fail to detect a theft.
So, the probability that none of the systems detect the theft is (0.01)^4 = 0.00000001.
Subtracting this from 1 gives us the probability that at least one system will detect the theft: 1 - 0.00000001 = 0.99999999.
So, the probability that at least one of the four systems will detect a theft is approximately 1, or 100%.
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