Khanacademy teaches us how to handle simple inequalities (less than or more than). In an equation, we usually have one solution. In problems involving inequalities, there is a whole set of answers. For instance, x minus five is less than 35. The answer for x is a whole series of numbers that when five is taken away from it, is less than 35. This equation is handled like any other equation involving an equal sign. We add five on both sides of the equation and the answer for x is any number that is less than 40 (35 plus five). To help us visualise the problem, a number line is used to illustrate the solution.