The Cannibals of an Island have the habit of eating each other.
One evening, the cannibals threw a dinner party. Six cannibals turned up and they decided to eat each other in turn. So someone was selected for everyone to eat (except the victim!), and when he had been eaten, someone else was selected, and so on.
If it took one cannibal two hours on his own to devour one person, how long was it before just one consumer remained?
When Cannibal #1 comes out there are five of his compatriots to devour him.
Thus, it would take 2/5th of an hour to eat him.
When Cannibal #2 comes out, there are four of his compatriots to eat him. This would take: 2/4th of an hour to do so.
When Cannibal #3 comes out, there are three of his compatriots to eat him, which would take 2/3 rd of an hour.
Accordingly, Canninal #4 and Cannibal #5 would be devoured in (2/2 + 2/1) hours.
Consequently, the entire process of devouring will take = (2/5+2/4+2/3+2/2+2/1) hours = 4 hours 34 minutes.