A man has 5 pieces of chain that must be joined into a long chain. He can open ring 3 (first operation), link it to ring 4 (second operation), then unfasten ring 6 and link it to ring 7, and so on.
He could complete his task in 8 operations, but he wants to do it in 6. How does he do it?
He opens all 3 rings of 1 piece (3 operations). With these, he links the other 4 pieces together. This will give a total of 6 operations.