Stage 10 · Percentages & speed
Speed
Distance = speed × time.
How to do it
Method
Distance = speed × time
60 km/h for 3 hours: 60 × 3 = 180 km
One more example
180 km at 60 km/h: 180 ÷ 60 = 3 hours
In full
Speed is how far you go in each unit of time: 60 km/h means 60 km every hour; 5 m/s means 5 m every second; 80 m/min means 80 m every minute. Of distance, speed and time, any two give the third: distance = speed × time; speed = distance ÷ time; time = distance ÷ speed. At 60 km/h for 3 hours: 60 × 3 = 180 km; 180 km in 3 hours: 180 ÷ 3 = 60 km/h; 180 km at 60 km/h: 180 ÷ 60 = 3 hours. Match the units: km/h with hours, m/s with seconds, m/min with minutes. If you forget, draw a triangle with distance on top and speed and time below, cover the one you want, and what's left is the sum.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
30 km at 15 km/h = ? h
Show the answer and working
Answer: 30 km at 15 km/h = 2 h
time = distance ÷ speed: 30 ÷ 15 = 2 h
Example 2
9 m/s for 23 s = ? m
Show the answer and working
Answer: 9 m/s for 23 s = 207 m
distance = speed × time: 9 × 23 = 207 m
Example 3
480 km at 120 km/h = ? h
Show the answer and working
Answer: 480 km at 120 km/h = 4 h
time = distance ÷ speed: 480 ÷ 120 = 4 h
Example 4
225 km in 3 h = ? km/h
Show the answer and working
Answer: 225 km in 3 h = 75 km/h
speed = distance ÷ time: 225 ÷ 3 = 75 km/h
Practise speed in the game →Stage 10 · Percentages & speed · Free to start, unlimited questions, no download