Harvard-MIT Math Tournament #0i06

Harvard-MIT Math TournamentHard

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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.

Triangle trigonometryTrigonometry

Problem

Problem:

Circles $C_{1}, C_{2}, C_{3}$ have radius $1$ and centers $O, P, Q$ respectively. $C_{1}$ and $C_{2}$ intersect at $A$ , $C_{2}$ and $C_{3}$ intersect at $B$ , $C_{3}$ and $C_{1}$ intersect at $C$ , in such a way that $\angle A P B = 60^{\circ}$ , $\angle B Q C = 36^{\circ}$ , and $\angle C O A = 72^{\circ}$ . Find angle $A B C$ (degrees).

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