Question 3
A pirate has five purses, each holding 30 coins. One contains only gold, another only silver, a third only bronze; each of the other two contains 10 gold,10 silver and 10 bronze coins. In each turn, one or more coins may be taken at random from a purse and examined. What is the minimum total number of coins needed to guarantee identifying the remaining contents of at least one purse? (5 points)
Source wording note: the supplied Vietnamese text permits turns as phrased above. The official original instead permits a single simultaneous choice of how many coins to take from each purse, only once. The answer is the same for both readings; the distinction is explained in the solution.
Neutral editorial illustration.
Source wording note: the supplied Vietnamese text permits turns as phrased above. The official original instead permits a single simultaneous choice of how many coins to take from each purse, only once. The answer is the same for both readings; the distinction is explained in the solution.
Neutral editorial illustration.