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, then it may increase or decrease.

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 11:30 and arrives in Portsmouth at 12:20.

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 = 50/60 which is simplified to 5/6 hour.

**Average Speed** = total distance ÷ total time

= 110 ÷ 5/6

= 110 × 6/5

= **132 **km/h

The average speed is 132 km/h

To test and consolidate your knowledge we'll use it to answer word problems!