There is a common formula in math that states that distance = rate x time. The rate is how fast the object is moving. If this car travels 55 mi. in 1 hour, then its rate is 55 mi/hr. To determine how far it will go in an unspecified number of hours, we can let t = time in hours. The letter t will be our variable. Assuming that the car travels at the same speed, we can state that the rate is 55, and that will be our constant. The expression would then be:
Distance of car traveled in t hours, which we can denote as D(t) = 55 x t = 55t
This means that D is a function of t, and D represents the total distance traveled in t hours.
