Khan Academy: Modular Addition and Subtraction

Beginning a "handful of fairly simple inequality videos," Sal demonstrates a few inequality problems in which mathematicians need to add or subtract. Though he states that his goal is to familiarize viewers with the notation, his...

Video showing how to add and subtract numbers using significant figures. Contrasts adding and subtracting with significant figures with multiplying and dividing. [8:59]

Video defining the addition rule for probability, including finding the probability of mutually exclusive events. [10:43]

Video defines what a polynomial is, identifies some different types of polynomials, explains how to determine the degree of a polynomial, shows how to add and subtract polynomials, and shows how to write polynomial expressions to...

Understanding modular multiplication and its proof as related to cryptography.

Understanding and finding a modular inverse.

Sal shows an example finding the relative complement or difference of two sets A and B.

Hypothesis Test for Difference of Means.

Demonstrates how to simplify an expression that involves both addition and subtraction of polynomials. [2:27]

This video teaches addition and subtraction of negative numbers using a number line. Practice problems are available. [9:16]