Topics / Maths
Speed, distance and time
Speed tells you how far something goes in a unit of time. The three quantities are linked: speed = distance ÷ time, distance = speed × time and time = distance ÷ speed. Most mistakes come from mixing minutes and hours.
What is tested
- Finding speed, distance or time from the other two
- Converting minutes to hours (30 min = 0.5 h, 20 min = 1/3 h)
- Average speed over a whole journey
Worked example
A train travels 150 km in 2½ hours. What is its average speed?
- Speed = distance ÷ time.
- 150 ÷ 2.5 = 60.
- The units are km per hour.
Answer: 60 km/h
Exam-day checklist
- Write the formula before substituting.
- Put the time in hours if the speed is per hour.
- Average speed = total distance ÷ total time.
- Check the answer is sensible (a walker is not 60 km/h).
Common mistakes
- Using 1.30 for 1 hour 30 minutes (it is 1.5).
- Averaging two speeds instead of using total distance ÷ total time.
- Multiplying when you should divide.
Try it yourself
1. A cyclist rides at 12 km/h for 40 minutes. How far does she go?
Show answer
8 km
40 minutes = 2/3 of an hour, and 12 × 2/3 = 8.
2. How long does a 45 km journey take at 30 km/h?
Show answer
1 hour 30 minutes
45 ÷ 30 = 1.5 hours.
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