Calculations of speed (or other compound measures) is easier if the magic triangle method is used.

This method avoids transposition of formulae (Changing the subject).

Another trick is for pupils to remember that speed is in km / h i.e. distance / time.

It is important that pupils realise that average speed is a measure of total distance divided by total time.

e.g. An object travels at a speed of 1 m/ s for 2 seconds and 2 m / s for 5 seconds. Find the average speed of the journey in metres per second.

The total time is 2 + 5 = 7 seconds.

The total distance must be calculated.

distance = speed x time

1st part distance = 1 x 2 = 2 m

2nd part distance = 2 x 5 = 10 m

Total distance = 12 m

Average speed = 12 ÷ 7 = 1.7 m / s ( 2 s.f.) (see Rounding)