I recently had a student writing to me asking for advice on problem-solving. The
student gave a few examples of problems they didn’t solve (like I
tell people to). One of the
things that struck me about the message was their description of their work on
USAMO 2021/4, whose statement reads:
A finite set S of positive integers has the property that,
for each s∈S, and each positive integer divisor d of s,
there exists a unique element t∈S satisfying gcd(s,t)=d.
(The elements s and t could be equal.)
Given this information, find all possible values for the
number of elements of S.
Roughly (for privacy reasons, this isn’t exactly what …
Sometimes I get asked broad advice questions on solving problems, for example
questions like:
- How do I know when to switch or prioritize approaches I come up with?
- How do I know which points or lines to add in geometry problems?
- How can I tell if I’m making progress on a problem?
- How can I guess the answer if “find all” or “find min/max” problems?
- How can I tell whether a conjecture I made is true or not?
- What should I do on a problem when I am stuck?
and so on.
I think all of these questions have a certain quality that, for lack of a better
name, I’ll dub as being “NP-hard”.
This is a bit of abuse of terminology borrowed from
complexity theory,
but let me explain why I think the name fits.
We know that solving math problems is generally difficult.
There’s …
So I have an FAQ now for contest-studying advice, but there’s a “frequently used
answer” that I want to document now that doesn’t fit in the FAQ format because
the question looks different to everyone that asks it.
The questions generally have the same shape: “would it be better to do X or Y
when studying?”. Like:
- Is it better to use GeoGebra when practicing geometry?
- Should I work on some new OTIS units or go back through some old ones that I
didn’t finish?
- Should I work on hard problems in my strongest subject or medium problems in
my weaker subjects?
- Would it be better if I learned this or that first?
and things like this.
And the answer is, for a lot of pairs (X,Y), if you’re so unsure that you’re
asking me about it, then you should just do whatever you …