This chapter discusses equations and inequalities. An equation that is not an identity is called a conditional equation. Sometimes identities are called formulas. However, usually, the word formula is used for an equation in which the letters involved denote physical or geometrical quantities. The easiest way to solve an equation is by inspection—if the equation is simple enough. For solving harder equations, the strategy is to keep modifying the equation until one arrives at some equation that can be solved. The chapter review two of the simplest types of equations, namely, linear and quadratic equations. Algebra can be used to solve a variety of practical problems from the natural sciences, the social sciences, and technology. The solution of a problem involves two steps: (1) set up and (2) solution. An important relation in the real number system is called order. This relation asserts that one number is less than, or greater than, another. The set of all numbers between two fixed numbers is a segment on the number line. Absolute values have an important geometric meaning on the number line. Relationship between algebra and geometry is important. Sometimes geometric problems can be attacked algebraically, and sometimes vice versa.