Introduction to Functions
We often describe one quantity in terms of another. Consider the following.
a. The amount of your paycheck if you are paid hourly depends on the number of hours you worked.
b. The cost at the gas station depends on the number of gallons of gas you pumped into your car.
c. The distance traveled by a car moving at a constant speed depends on thetime traveled.
We can use ordered pairs to represent these corresponding quantities. For example, we indicate the relationship between the amount of your paycheck and hours worked by writing ordered pairs in which the first number represents hours worked and the second number represents paycheck amount in dollars. Then the ordered pair (5, 40) indicates that when you work 5 hr, your
paycheck is 
80 paycheck and working 20 hr results in a $160 paycheck.