Speed is an example of a compound measure, which is one that involves more than one unit of measurement.

Speed is a measure of distance (e.g. miles, km) in relation to time (e.g. hours, minutes) and can be measured in mph (miles per hour), km/h etc....

Throughout a typical journey, speed varies. It stays constant, it increases and it decreases.

We calculate the average speed from the total distance travelled and the total time taken.

Average Speed = Total distance travelled ÷ Total time taken

**Example**

A train leaves London at 1130 and arrives in Portsmouth at 1220. The distance between the two stations is 110 km. Find the average speed in km/h.

**Answer**

First we must state the time taken in hours, not in minutes.

Time taken = 50 minutes = 5/6 hour

**Average Speed** = Total distance ÷ Total time = 110 ÷ 5/6 = 110 × 6/5 = **132 **km/h