Quote:
Originally Posted by pdurrant
OK, a quick logical/mathematical one. (Thanks, Dara O Briain!)
A bank is implementing security on their main vault. There are four people authorised to hold keys for the vault, and the bank wants any three of the four keyholders to be able to open the vault together, but any two people must not be able to open the vault on their own.
What is the minimum number of separate locks the vault must have, and how must keys be assigned to the four key holders?
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From the School of Hard Sums (or similar)? I've been watching that series, but must have missed that episode. Hang on while I check i-Player
