If we identify two quantities in a problem and one quantity is proportional to the other, then we can calculate the constant of proportionality and use it to answer other questions about the situation. For example, Andre runs at a constant speed of 5 meters every 2 seconds. How long does it take him to run 91 meters at this rate?

To find a value in the right column, we multiply the value in the left column by $\frac25$ because $\frac25 \boldcdot 5 = 2$. This means that it takes Andre $\frac25$ of a second to run 1 meter.

At this rate, it would take Andre $\frac25 \boldcdot 91 = \frac{182}{5}$, or 36.4, seconds to walk 91 meters. More generally, if $t$ is the time it takes to walk $d$ meters at that pace, then $t = \frac25 d$.