Units
It is important that, for all of these calculations, the units used are consistent.
If the distance is given in kilometres and the time in hours, then the measurement of speed should be given in the form of kilometres per hour. This is written as \(km/h\).
This next question shows where you need to be careful with units.
Question
Kelly runs from \(4.50pm\) until \(5.20pm\) at an average speed of \(7km/h\).
How far did she go?
\(4.50pm - 5.20pm = 30 mins\)
However, the speed is given in \(km/h\), so our time must be given in hours.
\(30 mins = 0.5 hr\)
\(Distance = Speed \times Time\)
\(Distance = 7 \times 0.5\)
\(Distance = 3.5\,km\)
Kelly ran \(3.5km\)