## The Basics of Direct Proportion

A car travels at 40 kilometers per hour traveled for 7 hours. The table of the distances traveled with respect to time is shown below.

Observe the relationship between the distance traveled and the time. As the time increases, the distance traveled increases. If the number of hours increases two times, then the distance also increases two times. Between hour 1 and hour 2, the increase in time is 1 hour, and the increase in distance is 40 kilometers. Between hour 3 and hour 5, the increase in time is 2 hours, and the increase in distance is 2(40) = 80 kilometers.

If there are two changing quantities $x$ and $y$ and if the value of $x$ changes 2 times, 3 times, and so on, $y$ also changes 2 times, 3 times, and so on respectively, we can say that $y$ is directly proportional to $x$. In the relationship above, distance is directly proportional to time.  » Read more