Speed and other rates · Grade 7
In Grade 7 you learn: speed, distance and time.
A rate compares two different quantities, such as kilometres per hour, litres per minute or words per minute. Speed is the most common rate: it links distance, time and how fast something moves.
Key facts
- Speed = distance ÷ time; distance = speed × time; time = distance ÷ speed.
- For km/h, use the time in hours: 15 min = 0.25 h, 20 min = 1/3 h, 45 min = 0.75 h.
- Average speed = total distance ÷ total time — not the average of the speeds.
- Every rate works the same way: amount = rate × time.
Worked examples
Example 1
A train travels 270 km in 2 hours 15 minutes. What is its average speed?
Answer: 120 km/h
Example 2
A coach drives for 2 hours at 60 km/h, then 1.5 hours at 100 km/h. Find the average speed for the whole journey, to 1 decimal place.
Answer: 77.1 km/h