It is known that a safe has more locks and controls the key by 5 persons. No 3 person can open the safe, and any 4 can open the safe,Ask the safe how many locks there are
Second men holding keys for locks 1, 5, 6, 7. Third men holding keys for locks 2, 5, 8, 9, fourth holding keys for locks 3, 6, 8, 10, and fifth holding keys for locks 4, 7, 9,, 10
The answer is 10 locks, for example, the first person holds the keys of the 1, 2, 3 and 4 locks
The key to any lock is only two people holding it, and any two people have the same key. The lock is the least needed
