Here it is, the chapter's best secret: on a distance–time graph, the slope IS the speed. Rise is kilometres gained, run is hours spent, so rise over run comes out in kilometres per hour. A steeper line is simply a faster trip — you can rank three cyclists at a glance without computing a thing.

The formula is the slope formula on wheels: $v = \dfrac{d}{t}$ — read aloud, v equals d over t — where $d$ is the distance travelled (kilometres), $t$ is the time it took (hours), and $v$ is the speed that comes out, in km/h. Rearranged for whichever piece is hiding: $d = vt$ (a speed held for a time covers ground) and $t = \dfrac{d}{v}$ (the trip divided by your pace). Keep the units matched — kilometres with hours — and the answers come out as clean as the draws in this lesson.