Speed, distance and time questions are reliable marks once you avoid two traps: mixed units and averaging speeds.
The one formula
- Distance = speed × time
- Time = distance ÷ speed
- Speed = distance ÷ time
Units
If the speed is in km/h, the time must be in hours. 45 minutes is 0.75 hours, and 20 minutes is one-third of an hour. To turn hours into minutes, multiply by 60.
The average-speed trap
Driving 60 km at 60 km/h and 60 km back at 30 km/h does not average 45 km/h. Time out = 1 hour, time back = 2 hours, total 120 km in 3 hours = 40 km/h.
💡 Write the units next to every number. If you end up with km/min, you know a conversion is missing.