Email   Blog   Facebook   YouTube   Twitch   Discord   Github


  •  CV
  •  Photos

Teaching (OTIS)


  •  For beginners
  •  Problems
  •  MOP
  •  ELMO
  •  USEMO


  •  Puzzle hunts
  •  Twitch
  •  Discord

plz learn code

  •  Filesys
  •  Learning path


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



  •  Mentors
  •  Quotes
  •  Rec letters
  •  FAQ's

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.1

New: Thanks to the great work of Rustam Turdibaev and Olimjon Olimov, we now have a enormous 336-problem index of recent problems by subject and MOHS rating. In addition, the linked file also contains a hyperlink to each of the corresponding solution threads on Art of Problem Solving.

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. In particular, I tend to be more terse than other sources.

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. The Math Magazine has recently resumed publishing yet another version of the problems and solutions of the olympiad.

See some statistics for recent years.

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.


In high school, I and some others ran an online contest called the NIMO (National Internet Math Olympiad) as well as one called the OMO (Online Math Open). Neither contest is active at the time of writing (April 2021) but I collected all the materials and put them in a Google Drive link since the website for that contest is not currently online. Most of the problems are short-answer problems.

  1. The acronym stands from “math olympiad hardness scale”, pun fully intended

Updated Wed 13 Oct 2021, 16:36:27 UTC by 01e62a047199