Email: evan  [at] evanchen•cc


  •  Résumé

Teaching (OTIS)


  •  Problems
  •  ELMO
  •  For beginners



  •  EGMO book
  •  Napkin (v1.5)
  •  Course notes


  •  Blog
  •  Facebook
  •  Youtube+Twitch



  •  FAQ's
  •  Rec letters

Buy Me a Coffee at

Olympiad Problems and Solutions

This page contains problems and solutions to several USA contests, as well as a few others.

Hardness scale

Here is an index of many problems by my opinions on their difficulty and subject matter. The difficulties are rated from 0 to 50 in increments of 5, using a scale I devised called MOHS. (The acronym stands from "math olympiad hardness scale", pun fully intended).

This document will probably see a lot of updates. Anyways, I cannot repeat enough the disclaimer that the ratings (and even philosophy) are my own personal opinion, rather than some sort of indisputable truth.

USA Math Olympiad (USAMO)

Despite being part of the USA team selection process, these are not the "official" solution files, rather my own personal notes. My understanding is that the internal problems and solutions, from the actual USA(J)MO committee, are copyrighted by MAA. To my knowledge they are not published anywhere.

USA TST Selection Test (TSTST)

For an explanation of the name, see the FAQ on the USA IMO team selection.

USA Team Selection Test (TST)

These exams are used in the final part of the selection process for the USA IMO team.

International Math Olympiad


Also listed on the USEMO page.


See also general ELMO information.

Taiwan Team Selection Test

These are the problems I worked on in high school when competing for a spot on the Taiwanese IMO team. These problems are in Chinese; English versions here.

Last modified: Sun Sep 27 21:28:33 2020.