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Math Olympiads - http://cage.rug.ac.be/~hvernaev/olympiad.html
Collection of problem sets from International and National Mathematics Olympiads. |
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Olympiad Math Madness - http://www.geocities.com/CapeCanaveral/Lab/4661/
Jeffrey Lockshin's collection of mathematical problems, invented for mathematical olympiads all over the world. |
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Problem Page - http://www.math.wisc.edu/~talent/problems.html
Archive of problem sets and solutions from Wisconsin Mathematics, Engineering and Science Talent Search. |
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Tournament of Towns at Toronto - http://www.math.toronto.edu/oz/turgor/archives.php
Contest problems and solutions for The International Mathematics Tournament of the Towns. |
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Prof. W. Kahan's Notes and Problems - http://www.cs.berkeley.edu/~wkahan/MathH90/
Large archive of problems and solutions from Professor Kahan's Putnam Problems Practice Seminar. |