Time, Speed & Distance • Topic 1 of 4

Speed, Time & Distance

Use distance = speed x time and keep units consistent. Convert km/h to m/s with 5/18 (and back with 18/5). For a fixed distance, speed and time are inversely proportional: if speed becomes 3/4, time becomes 4/3. This inverse logic answers 'late/early' problems: a known change in speed produces a known change in time over the same route.

✅ Solved examples

1. A car covers 240 km in 4 hours. Its speed?
240/4 = 60 km/h.
2. Convert 72 km/h to m/s.
72 x 5/18 = 20 m/s.
3. At 5/6 of his usual speed a man is 10 min late. Usual time?
Time becomes 6/5 of usual, so extra 1/5 of usual time = 10 min -> usual time = 50 min.
4. A man walks at 4 km/h and reaches 5 min late; at 5 km/h he is 10 min early. Distance?
Time difference = 15 min = 1/4 h. d/4 - d/5 = 1/4 -> d/20 = 1/4 -> d = 5 km.

✏️ Practice — try these, take hints as needed

1. Cover 150 km in 2.5 h. Speed?
d/t.
150/2.5.
—
60 km/h
2. Convert 90 km/h to m/s.
x 5/18.
90 x 5/18.
—
25 m/s
3. Convert 15 m/s to km/h.
x 18/5.
15 x 18/5.
—
54 km/h
4. At 3/4 usual speed, 20 min late. Usual time?
Time becomes 4/3.
Extra 1/3 = 20.
—
60 min
5. Distance if 6 km/h is 6 min late and 8 km/h is 4 min early?
Diff = 10 min = 1/6 h.
d/6 - d/8 = 1/6.
d/24 = 1/6.
4 km

📝 Topic test — 8 questions

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