The category of equations, known as direct variation, share a special relationship. Equations with direct variation may be expressed in the form y = kx and can be used to represent many different situations that occur in daily life. An equation of this form is special because the value of k is set. For example, if you earn $12.00/hr at a job, you can represent this as y = 12x. In the equation, the value 12 stays constant, while the values of x and y change. Anytime you want to compute your earnings, you simply substitute in the number of hours you work for x and your total earnings, y, will be known. Other examples where direct variation can be used is in computing distances (miles per hour) and costs (dollars per gallon).

In each situation described, you will be given the value of two variables and will need to solve for the third variable, that is, in some cases, you may have to solve for the variable k, y, or x. Try working each problem with paper and pencil first and then use the interactive application to check your solutions. To use the application, click on the "play" button and enter your values into the appropriate boxes. You may have to hit the "enter" key after you enter your values in order to refresh the application.