Speed, distance and time

How to use it

1. 1Check the units agree before dividing: km with hours gives km/hour, metres with seconds gives m/second.
2. 2When one of the three quantities is shared by two journeys, write both equations and eliminate it.
3. 3For a journey in stages, add the distances and add the times; the overall speed is their quotient.

Step-by-step

1. 1
   $\text{speed}=\frac{45}{3}=15$ km/hour

   Why: Divide distance by time to get the constant speed.

2. 2
   $\text{time}=\frac{75}{15}=5$ hours