Who Should Take This Course

This course is for students who are looking for a fun, challenging, and systematic introduction to the fascinating world of Combinatorics, which is not covered in depth in most school curricula, but which appears throughout middle and high school math competitions. This course will give you the main tools you need, in one month. To take this course, students should have successfully completed our Module 1: Algebra Basics course, or have skipped over it due to prior background.

This course will be understandable by anyone with a solid background in Pre-Algebra, and the willingness to concentrate on a single math problem for several minutes. At the same time, even high school students (who have not yet taken classes outside of school in Combinatorics) will learn a significant amount. Not recommended for students who can already score 17+ on AMC 8. Still not sure if this is the right course? Feel free to contact us at course-consulting@poshenloh.com to discuss.

How To Use This Course

The best way to build creative thinking skills is to play with challenging new problems every day, especially those for which you don’t know how to start. This course, which can be finished in 1 month, constitutes of 16 Daily Challenges and Weekly Challenges. Each Daily Challenge has two related math problems and their explanations. Don’t worry if they look unfamiliar. Just use the whole time during the problem videos (and hints) to think. You’ll get to invent your own strategies, which is the fun part!

Even if you figure out how to do a problem yourself, watching its explanation video is still very beneficial. It will show multiple interesting ways to do the problem, and introduce deeper ideas in math using everyday language. This brings advanced math down to earth.

There is only one practice problem in each Daily Challenge (the “Your Turn” problem), and there aren’t any homework problems. This is because the way to learn how to solve the widest variety of problems is to learn how to invent your own solution methods! So, we encourage you to solve new problems all on your own instead of working on repetitive exercises. You’ll spend the same time on fewer problems, every one of which needs fresh creativity.

After every four Daily Challenges, we revisit the topics (with some twists), through a Weekly Challenge problem set that lets you focus uninterrupted for 40 minutes, on a variety of specially designed questions. After doing the problems, please read the explanations, even for the problems you solved. There are a lot of fun math coincidences and insights hidden in the problems.

We recommend pacing the course so that you can play with this flavor of mathematical thinking for a bit of time almost every day. 

The standard pace is to pick four days each week for four Daily Challenges, plus one hour on the weekend for the Weekly Challenge. If you think this pace is not challenging enough, feel free to double the pace, so that you can finish eight Daily Challenges and two Weekly Challenge each week.


Po-Shen Loh is a social entrepreneur, working across the full spectrum of mathematics and education, all around the world. He is the founder of the free personalized learning platform expii.com, an education technology social enterprise which algorithmically curates openly licensed math/science lessons and problems contributed by the world. Sales of these online courses support the development of these social initiatives.

Loh draws from his experience as a mathematics professor at Carnegie Mellon University, and also as the national coach of the USA International Mathematical Olympiad team. His research and educational outreach takes him to cities across the world, reaching over 10,000 people annually through public lectures and in-person events, and he has featured in or co-created videos totaling over 5 million YouTube views.

He has been continually involved in math competitions since he was a contestant in the late 1990's: when he ranked 3rd at the National MATHCOUNTS competition, and won a silver medal for the United States of America as a contestant at the International Mathematical Olympiad. He can be followed on Instagram (@poshenloh), Twitter (@poshenloh), WeChat (罗博深数学), and Weibo (poshenloh / 罗博深).

Po-Shen Loh

Math Professor