"one day a customer brought into the shop of abdul the jeweler six chains, each of which had five links. he wanted the six chains to be joined into one large circular chain and inquired as to the cost. 'well', replied the jeweler, 'every link i cut open and close costs one piece of silver.' .... how many pieces of silver are required for the job?"
disclaimer: i came up with a different answer than the one given in the book. granted, mine is a bit of a "backdoor" one, but i stand by it nonetheless.
submit your answer in the comments, and i'll confirm the correct one (and mine too). don't look at the comments unless you want to see the answer!