OTIS-Excerpts (2)

The OTIS Excerpts
A collection of 192 problems and solutions
Evan Chen
August 6, 2022
web.evanchen.cc/excerpts.html

The noblest art is that of making others happy.
P. T. Barnum
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©2019 Evan Chen. All rights reserved. Personal use only.

Preface
This book is a selection of notes from twelve of the lectures that I use in
my year-round math olympiad classes. The program is affectionately named
OTIS. The abbreviation officially stands for “Olympiad Training for Individual
Study”; but in truth, I rigged the acronym so that it would match the name
of an elevator in Lincoln, Nebraska of which I had fond childhood memories.
When I started teaching OTIS back in the fall of 2015, it was just a small
group of students at Phillips Academy that I would meet with every couple of
weeks. Despite my inexperience at the time, I have fond memories of this first
group, and I maybe learned as much from them as they did from me.
Every year since then, the number of OTIS students has doubled, and the
number of applications has increased even faster than that. At the same time,
I became increasingly involved with volunteering with the organization of high-
school contests. By the time I started graduate school, I was spending so little
time on my own studies that I began to fear (rightly or wrongly) that I might
fail out of the math PhD program.
Thus, despite my best efforts, I eventually had the heartbreaking task of
having to tell eager and enthusiastic students that I simply did not have the
time or space to take them all under my wing. I am the kind of person who
finds it hard to say no, and so this was painful for me to do. OTIS taught me
the reality that I am just one person.
In this way, these notes are an apology to everyone I turned down, and to
everyone that I will have to turn down. I would have loved to be able to help
everyone who came to my doorstep. I am sorry that I could not do more, but
I wrote you a short book, as it was the least I could do.
As with all my works, there are bound to be numerous errors, mistakes,
or points of unclarity. Comments, suggestions, corrections are very welcome.
You can reach me at [email protected].
Evan Chen
December 30, 2018
Fremont, California, USA
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