This site teaches Arithmetic with Polynomials and Rational Expressions to High Schoolers through a series of 4333 questions and interactive activities aligned to 26 Common Core mathematics skills.

This site teaches High Schoolers how to create equations through a series of 298 questions and interactive activities aligned to 5 Common Core mathematics skills.

This site teaches Reasoning with Equations and Inequalities to High Schoolers through a series of 5909 questions and interactive activities aligned to 36 Common Core mathematics skills.

This site teaches Structure in Algebraic Expressions to High Schoolers through a series of 3482 questions and interactive activities aligned to 26 Common Core mathematics skills.

Allele frequencies in populations and how they differ from genotype frequencies. Created by Sal Khan.

A gene as a stretch of DNA on a chromosome. Alleles as versions (sequence variants) of a gene.

Outline of the 1973 Allende Coup in Chile and Pinochet's Junta (this video under CC-BY-SA). Created by Sal Khan.

There are a number of European alliances that contributed to the broad scope of World War I. Prominent among these are the 1839 Treaty of London, which promised that the United Kingdom would protect Belgium's neutrality, the 1879 Dual Alliance treaty between Germany and Austria-Hungary to protect each other in the event of Russian attack, the 1892 Franco-Russian Military Convention that promised mutual assistance in the face of attack, the Triple Entente linking the United Kingdom and France (and later Italy), and the Triple Alliance linking Germany, Austria-Hungary, and Italy (at first). Created by Sal Khan.

How the Chinese buying of American debt leads to lower interest rates. Created by Sal Khan.

Core beliefs around the role of government in the US. Discussion of quotes by Ronald Reagan, FDR, Barack Obama and Milton Friedman.

Unlike European option, an American options can be exercised at any point before it expires. In this video we walk through the process of exercising an American call option. Created by Sal Khan.

In 1944, the Americans (and Allies) make even more progress in the Pacific. By the end of the year, they have taken positions that put them within bombing range of Japan.

In 1944, the Americans (and Allies) make even more progress in the Pacific. By the end of the year, they have taken positions that put them within bombing range of Japan.

Unlike European option, an American options can be exercised at any point before it expires. In this video we walk through the process of exercising an American put option. Created by Sal Khan.

An example of simplifying a seemingly complicated resistor circuit. Created by Willy McAllister.