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Grade Vs Difficulty:

A collection of problems in number theory, including an exploration of the Euclidean Algorithm.
Also includes a discussion of the abc Conjecture, a topic that had been in the news (e.g. feature article in the New York Times) around the time this session was presented (November 2012 at the San Diego Math Teachers' Circle).
Includes solutions and session leader notes.
The Euclidean algorithm is an important part of the Rational Tangle activity.
There is a second activity in the lesson plan section that has easier questions related to the Euclidean algorithm. See
LCM, GCD.