How it works

Speed, distance and time are linked by speed = distance ÷ time, which can be rearranged to find distance = speed × time or time = distance ÷ speed. A formula triangle can help rearrange the equation. Units must be consistent, so conversions between hours and minutes, or kilometres and metres, are often required before or after calculating.

The method

1. 1.Identify which quantity is unknown: speed, distance or time
2. 2.Choose the correct rearrangement of speed = distance ÷ time
3. 3.Convert units so they are consistent throughout
4. 4.Substitute values and calculate

Worked example

A car travels 150km in 3 hours. Find its average speed.

1. Speed = distance ÷ time
2. Speed = 150 ÷ 3 = 50 km/h

Worked example

A cyclist travels at 20km/h for 45 minutes. Find the distance travelled.

1. Convert 45 minutes to 0.75 hours
2. Distance = speed × time = 20 × 0.75 = 15km

Common mistakes

• Using inconsistent units, such as mixing minutes and hours without converting
• Rearranging the formula incorrectly when finding time or distance
• Forgetting to convert the final answer to the units requested