Solve for speed, distance, or time — enter the two you know.
The relationship is a single equation rearranged three ways: speed equals distance divided by time, distance equals speed times time, and time equals distance divided by speed. That much is easy. Nearly every wrong answer comes not from the formula but from mismatched units, because the units must agree before the arithmetic means anything.
If speed is in kilometres per hour, time must be in hours and distance in kilometres. Feeding in minutes without converting is the classic error: 30 minutes is 0.5 hours, not 30. A second trap is averaging speeds. If you drive one leg at 60 km/h and an equal-distance leg at 40, your average is not 50 — you spend more time on the slower leg, so the true average is 48, the harmonic mean. Average speed is always total distance divided by total time, never the arithmetic average of the speeds, and this matters whenever a journey is split into unequal segments.
Almost always a unit mismatch, usually minutes entered where hours were required. If the speed is per hour, convert time to hours first: 45 minutes is 0.75 hours.
No. Average speed is total distance divided by total time. For equal distances at different speeds the correct figure is the harmonic mean, which is always lower than the arithmetic average because more time is spent at the slower speed.
Divide km/h by 3.6 to get m/s, and multiply m/s by 3.6 to go back. The factor comes from 1,000 metres divided by 3,600 seconds.
No. These formulas assume constant speed. Where speed changes, they give an average over the whole journey rather than the speed at any given moment, and acceleration needs its own equations.