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MathNet 2026 — Part 06 Question 129

Math Olympiad Vault · MathNet 2026 — Part 06

Question 129

Caitlin and Donal play a game called *Basketball Shoot-Out*. The game consists of 10 rounds. In each round, Caitlin and Donal both throw a ball simultaneously at each other's basket. If a player's ball falls into the basket, that player scores one point; otherwise, they score zero points. The scoreboard shows the complete sequence of points scored by each player in each of the 10 rounds of the game.
It turns out that Caitlin has scored at least as many points in total as Donal after every round of the game. Prove the number of possible scoreboards is divisible by 4, but is not divisible by 8.