A bag contains discs of three colours: 7 red, 8 blue and 9 yellow. Two discs are drawn at random. If the drawn discs are the same colour, they are put back into the bag. If the drawn discs are different colours, they are removed and a disc of the third colour is placed into the bag. This procedure is repeated until only one disc is left in the bag, or all remaining discs are of the same colour. What colour is the last disc (or discs) left in the bag?
Sign in or create an account to reveal answers, view the solution, and save your progress. Create a free account to unlock practice and keep track of your work.
Cayley Mathematical Olympiad (2023)
One puzzle per day. Cryptarithm, Magic Square, Summit. No sign-up required to play.
Play daily puzzle →Interactive problems and curated lessons—water pouring, magic squares, knight's tour, and more.
Browse library →See how you rank. Top solvers by problems solved correctly. Sign in to climb the ranks.
View leaderboard →