If the probability of seeing a car is 609/625, then the probability of NOT seeing a car is 1 - 609/625 = 16/625.
This means that if we must not have seen a car in each of FOUR five minute periods. So we must multiply the likelihood of NOT seeing a car in each five minutes, *x* (4 times) and get 16/625.
x^4 = 16/625
x = 2/5
Since the question asked about the likelihood of SEEING a car in 5 minutes, we must subtract that likelihood from 1...
1 - 2/5 = **3/5**, the answer.
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Problem found at:
http://www.techinterview.org/Puzzles/carsontheroad.html |