Chapter 8
Speed, Distance & Time
S = D ÷ T, average speed, meeting points, multi-leg journeys
8.1 The core formula
Speed = Distance ÷ Time Distance = Speed × Time Time = Distance ÷ Speed
All three variables must be in consistent units. Convert mixed times to decimal hours: 2h 15min = 2.25h, 48min = 0.80h.
8.2 Finding arrival time
Travel time = Distance ÷ Speed Arrival = Departure + Travel time
Example: departs 07:40, 210 km at 84 km/h. Travel time = 2.5h = 2h 30min. Arrival = 10:10.
8.3 Average speed
Average speed = Total distance ÷ Total elapsed time
Includes all rest stops. Never average individual leg speeds directly. Example: 80 km at 40 km/h + 30min rest + 120 km at 60 km/h. Avg = 200 ÷ 4.5 ≈ 44.4 km/h.
💡 Adding rest time to the denominator always reduces the average speed below the moving-only average.
8.4 Time saved by increasing speed
Time saved = Scheduled time − Actual time Net delay = Total delays − Time saved
Example: 450 km normally at 150 km/h (3h). Departs 20min late, 10min stop, travels at 180 km/h (2.5h). Time saved = 30min. Net delay = 30 − 30 = 0.
8.5 Two vehicles travelling toward each other
Head-start distance = Speed_A × (time between departures) Remaining gap = Total distance − Head-start Combined speed = Speed_A + Speed_B Time to meet = Remaining gap ÷ Combined speed
Example: Car A at 09:00 (75 km/h), Car B at 10:00 (105 km/h), 390 km apart. Head-start = 75 km. Gap = 315 km. Combined = 180 km/h. Time = 1h 45min. Meet at 11:45.