A searchlight on top of the watch-tower makes 1 revolutions per minute. What is the probability that a man appearing near the tower will stay in the dark for at least 20 seconds?	Choose the correct answer
A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4
1 revolutions per minute = 1 revolution every 60 seconds   So no matter what anybody appearing at the tower cannot stay in the dark for more than 60 seconds. This will be our total number of possibilities i.e the denominator.   P(man in dark for at least 20 seconds) = 1 - P (man in dark for max of 20 seconds) = 1 - 20/60 = 1 - 1/3 = 2/3   or the other way would be:   P(man in dark for at least 20 seconds) is like saying he can be in dark for 5,6,7...all the way to 60 seconds because that is the max. In this approach it would be 20/60 seconds = 1/3.   Answer is 1/3
<result>B</result>
A searchlight on top of the watch-tower makes 1 revolutions per minute. What is the probability that a man appearing near the tower will stay in the dark for at least 20 seconds?