There are many locks and 9 people. At least 5 people are needed to open all the locks. If the number of locks is small as possible, how many keys does each person have?
Details and Assumptions
- Each lock needs a different key.
- Each key has many copies.
- Every group of 5 people is able to open all the locks
- This question is in memory of the mathematician Augusto C. O. Morgado.