About Harim Yoo

Harim Yoo


The author, Harim Yoo, graduated from Northwestern University with (B.A. in Mathematics / Economics) in 2012. Harim also served in the ROK/U.S Army as a KATUSA sergeant in the 2nd infantry division from 2012 to 2014. Since his ETS from duty, he found his passion for teaching and educating bright students in South Korea, who are planning to apply to universities(or colleges) in the States.

He gradually developed his career as a lecturer at MASTERPREP and has now been working as a director of REACHPREP in Apgujeong, Seoul. Harim spent time writing books on math competitions and prep books for high school mathematics in the United States.

Inspired by Scott Young, a pioneer of ultra-learning, he initiated a project of learning the frontend coding - HTML, CSS, Javascript, Python, and Flask - at the age of 33, and built HARIMATH to facilitate efficient learning of mathematics, providing the full list of errata, more examples, and detailed explanations currently not in the prep-books.

The philosophy of teaching he believes in orients in searching for a solution path to a math problem. He believes that the progressive overload of procedure-based math problem solving practices will eventually turn students into creative problem-solvers when they labor in work force in future. That being written, most of the drills provided to students have only answers shown, not the full solutions.


  • Harry Park (B.S. in Vanderbilt University) : he majored in computer science and mathematics, providing sufficient help to build this website.
  • Gerald Ahn (B.S. in Georgia Tech) : he is currently majoring in industrial engineering,providing feedbacks to the problems and their solutions, regarding the problems' difficulties and the methods of problem-solving.