Placing Letters "X" and "O" on a Plane

Putnam 1993, A1

IMO 2005, Number Theory Shortlisted Problem

Putnam 1998, A2, A Geometry Problem in Two Ways.

Putnam 2021, A2; A Limit Problem from the 2021 Putnam Math Competition

Why is This Product a Perfect Square?

Sequence of Polynomials

A Diophantine Equation with a Slick Solution

Putnam 2023, B1; Interesting Combinatorics Problem from the 2023 Putnam Math Competition.

A Very Difficult Inequality Problem with an Elementary Solution

Putnam 2023, B2; A Neat Number Theory Problem from the 2023 Putnam Math Competition.

Putnam 2023, A3; A Very Challenging Putnam Calculus Problem!

Putnam 2023, A2; Solution to a Polynomial Problem from the 2023 Putnam Math Competition.

Putnam 2023, A1; Solution to a Calculus Problem from 2023 Putnam Math Competition

Can You Solve This Divisibility Problem Involving Combinations?

Challenging Geometry Problem in Two Ways; 2023 UMD Math Competition, Part 2, Problem 2

A Fun Combinatorics Problem; University of Maryland High School Math Competition, Part 2, Problem 2

A Counting Problem in Two Different Ways; IMC 2020, Problem 1

Can You Solve This System?

A Challenging Pigeonhole Principle Math Competition Problem!

A Very Challenging Number Theory Problem; Canadian Math Olympiad, 2021, Problem 4

IMO 2005, Problem 4; An Interesting Number Theory Problem.

A Challenging Algebra Problem; Putnam 2003, A4

IMO 1987, Problem 4; A Challenging Functional Equation Problem.

A Surprisingly Challenging Quadratic Polynomial Problem

A Challenging IMO Functional Equation Problem, IMO 1977, Problem 6

Putnam 2021, A1; How Many Hops Does the Grasshopper Take?

2023 AMC 12A; Solution to Problems 22, 23, 24, and 25

IMO 2021, An Interesting Number Theory Problem, Shortlisted, N3

Putnam 2003, A2; An Inequality Problem