Home
Book
Learn
Library
Practice
Contact
Log In
Tutorial
Analysis
Practice
Video
AMC
AMC10_12
2016 AMC10A #20
2008 AMC12B #22
2015 AMC12A #23
AMC8
2015 AMC8 #25
Combinatorics (Counting)
0 - Introduction
Introduction
Learning Guide
1 - Basic Principles
The Addition and Multiplication Principle
Application - Count and Sum An Integer's Divisors
Mind the Catches
Inclusion and Exclusion Principle (Venn Diagram)
Application - Euler's $\varphi$ Function
2 - Formulas
Permutation and Combination
Factorial Defined
3 - Techniques and Patterns
Count Like A Pro
The Lattice Method
Cut the Rope (Stars and Sticks)
Bundling and Symmetry
Derangement
Combining Permutation and Combination
Balls in Boxes
Recursion
4 - Elementary Probability
Probability Basics
The Tree Method
Geometric Probability
Probability Review
Example - 2015 AMC12A #23
Find the Correct Region
Application - Estimate $\pi$
Additional Topics
The Binomial Theorem
Pascal Triangle
Combinatorial Identities
General
Introduction to Math All Star Online Course
Become a Math Competition Pro
Look Beyond Obvious
Road Towards a Math Star
Generating Function
IMO
1975 IMO
1992 IMO
Indeterminate Equation
0 - Introduction
Introducation
1 - Basic Techniques and Patterns
The Factorization Method
Solving $\frac{1}{x}+\frac{1}{y}=\frac{1}{n}$
The Difference of Squares Method
Sum of Squares
2 - Intermediate Techniques and Patterns
Property of Symmetry
Solving $\frac{1}{x}+\frac{1}{y}=\frac{m}{n}$
Solving $\frac{1}{x}+\frac{1}{y}+\frac{1}{z}=\frac{m}{n}$
The Squeeze Method
The Quadratic Method
Pythagorean Triplet
Solve Linear Indeterminate Equation
3 - Advanced Techniques and Patterns
The Infinite Descent Method
Introduction to Pell's Equation
Solve Pell's Equation
The MOD Method
Number Theory
Square Numbers
A quick way to find the tens digit of $m^n$
USAMO
2015 USAMO