Fifty Lectures for Mathcounts Competitions (3);

Each lecture includes (1) Basic skills with examples, and (2) Exercises with answer keys.
Solutions to all practice problems can be found here:

http://www.amazon.com/Lectures-Mathcounts-Competitions-Solution-Manual/dp/1530806534
Training class is offered: http://www.mymathcounts.com/Copied-2014-Summer-Mathcounts-Training-Program.php