Saturday, 26 April 2014

Averaging Speed in Maths

Driving along, observing the speed limit and I entered a section of road covered by average speed cameras. I understand how these work and therefore know a driver should drive at a constant speed, at or under the speed limit, in order to avoid encountering a conviction. However, I observed a young lady speeding in between cameras and then slowing for each one. She clearly did not understand the term 'average'. This lead me to think about how 'average' could be taught using these cameras as a real life context.

I have two possible methods for carrying out this investigation:

One: Using the formula for calculating speed: Speed = Distance ÷ Time. Give the children a set of data. The data being that for time taken for drivers to travel the distance between cameras. The data can be put into the formula and then the children work out which motorists are within the limit and those who are not.

Image credit:

Two: Giving the children the driver's speed in between each camera on a road and then the children calculate an average of those speeds. Again, from this the children work out which motorists are within the limit and those who are not.

The first idea is more in line with how the system actually works. However, the second would work better in a primary classroom for calculating averages. We've made a resource to accompany the latter.

Also: See Stuart's very useful and helpful suggestions below

Update: February 23, 2015


  1. These cameras are a great opportunity for discussing average speed! It seems a slight shame to sacrifice 'reality' for the purpose of calculating averages. Couldn't the pupils calculate average times? Indeed, as a slight extension, they could look at subtracting times as that is, I'm guessing, the initial step of the real calculation.

    A more difficult extension question is the following: Cameras 1 mile apart. Speed limit 50mph. Motorist travels at 60mph for the first half mile. Is it possible for them to avoid a speeding ticket? What speed should they travel at for the remaining half mile? Simple distance/time or speed/time graphs could be drawn. You can even use speed cameras to introduce simple < and > inequalities (and IF.. THEN.. statements now that computing is more prominent). So much maths!

    And finally, "would you prefer a 20mph 'single' speed camera outside the school or a pair of 20mph average speed cameras?" would make for a nice debate.

  2. It's pretty easy to turn this into a real experiment too, with some hot wheels track and a couple of light sensors: