A searchlight on top of the watchtower makes 4 revolutions per minute. What is the probability that a man appearing near the tower will stay in the dark for at least 5 seconds?
Choose the correct choice from the following options:
A) 5 / 6  B) 4 / 5  C) 3 / 4  D) 2 / 3  E) 1 / 2

Rationale: the searchlight completes one revolution every 15 seconds . the probability that the man ' s area will be lit up is 5 / 15 = 1 / 3 . the probability that he will stay in the dark is 1 - 1 / 3 = 2 / 3 the answer is d .
Answer: D