摘要
Below is Problem 9 in Singapore MathematicalOlympiad 2001:Five people jointly bought a lottery ticketwhich won the first prize.They decided to keeptheir ticket in a locker installed with a number oflocks.Each person may hold the keys to more thanone lock.What is the minimum number of locks nee-ded to serve the purpose that any 3 together will beable to open the locker but any 2 of them togetherwill not be able to open it ?A.6 B.9 C.10 D.
Below is Problem 9 in Singapore Mathematical Olympiad 2001 ：
