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Berkeley Math Circle Monthly Contest 1 #0hlg

Berkeley Math Circle Monthly Contest 1Hard

From module Proof Writing Basics

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Understand the scale
Scale 0.5: Easiest math competition problems, often solvable even for early middle school students without experience. 1: Problems strictly for beginners, often at a moderate middle school level. 1.5: Problems for stronger beginner students, on the level of the middling problems in most middle school contests. 2: For motivated beginners, harder questions from the previous categories. 2.5: More advanced beginner problems, hardest questions from previous categories. 3: Early intermediate problems that require more creative thinking. 3.5: Tougher early intermediate problems that consistently stretch into higher-level creative thinking or conceptual knowledge. 4: Intermediate-level problems. 4.5: Upper intermediate problems approaching the upper bound for non-invitational sprint math competitions. 5: More difficult AIME problems or simple proof-based Olympiad-style problems. 6: High-level AIME-styled questions or introductory Olympiad-level questions. 7: Tougher Olympiad-level questions, may require more technical knowledge. 8: High-level Olympiad-level questions. 9: Expert Olympiad-level questions. 9.5: The hardest problems appearing on Olympiads which the strongest students could reasonably solve. 10: Historically notorious problems, generally unsuitable for even very hard competitions because they are exceedingly tedious, long, and difficult.
LogicAlgorithms

Problem

Problem:

A man has three pets: a mouse, a cat, and a dog. If the man leaves the cat and the dog alone, then the dog would kill the cat. If the man leaves the cat and the mouse alone, the cat would eat the mouse. One day the man decided to take his animals to the other side of the river. However, he has a small boat in which he can fit only one of the animals at a time. Show that it is possible for the man to take all of his animals to the other side of the river safely.

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