MathDB

4

Part of 1989 Chile National Olympiad

Problems(1)

N locks, 5 with some keys, any 3 may open it, no 2 can (Chile NMO 1989 P4)

Source:

11/19/2021
The vault of a bank has NN locks. To open it, they must be operated simultaneously. Five executives have some of the keys, so any trio can open the vault, but no pair can do it. Determine NN.
combinatorics