Time, Speed & Distance
Speed = Distance ÷ Time. Always check your units match before substituting.
A. Speed, Distance & Time
Speed
How fast something is moving — distance covered per unit of time.
FormulaSpeed = Distance ÷ Time
Distance
How far something has travelled.
FormulaDistance = Speed × Time
Time
How long the journey takes.
FormulaTime = Distance ÷ Speed
The SDT Triangle — Cover What You Want to Find
Example 1 — Car travels 240 km in 4 hours. Find speed.
1Speed = Distance ÷ Time = 240 ÷ 4
Speed = 60 km/h
Example 2 — Speed=80 km/h, Time=2.5 hrs. Find distance.
1Distance = Speed × Time = 80 × 2.5
Distance = 200 km
Example 3 — Distance=150 km, Speed=60 km/h. Find time.
1Time = Distance ÷ Speed = 150 ÷ 60
Time = 2.5 hours
Tip: Always check units match. If speed is km/h and distance is km, time comes out in hours. Convert minutes → hours by dividing by 60.
B. Time Conversions
Seconds → Minutes → Hours
60 seconds = 1 minute. 60 minutes = 1 hour. 3600 seconds = 1 hour.
Example2.5 hours = 2 hrs 30 min = 150 minutes = 9000 seconds
Days → Weeks → Years
7 days = 1 week. 14 days = 1 fortnight. 365 days = 1 year. 366 days = 1 leap year.
Example52 weeks = 1 year | 1 decade = 10 years | 1 century = 100 years
Leap Year Rule
Divisible by 4 → leap year. EXCEPT century years (1900, 2100) must be divisible by 400.
Example2000 → 2000÷400=5 → leap year ✓
1900 → 1900÷400=4.75 → NOT a leap year ✗
1900 → 1900÷400=4.75 → NOT a leap year ✗
C. 12-Hour vs 24-Hour Clock
Converting PM → 24-hour
Add 12 to the hours. Exception: 12:00 PM stays as 12:00.
Example3:30 PM → 3+12 = 15:30 | 9:15 PM → 21:15 | 12:00 PM = 12:00
Converting AM → 24-hour
Keep the same hours. Exception: 12:00 AM (midnight) becomes 00:00.
Example6:30 AM = 06:30 | 11:45 AM = 11:45 | 12:00 AM = 00:00
Converting 24-hour → 12-hour
If hours ≥ 13: subtract 12 and add PM. If hours ≤ 12: add AM (or PM for exactly 12).
Example15:45 → 15−12 = 3:45 PM | 08:20 = 8:20 AM | 00:00 = 12:00 AM
Example — Flight departs 22:30, lands 06:15 next day. Duration?
122:30 → midnight (00:00): 1 hr 30 min
200:00 → 06:15: 6 hr 15 min
3Total = 1hr30min + 6hr15min = 7 hrs 45 min
Flight duration = 7 hours 45 minutes
⚠ Common mistakes:
(1) Mixed units — if speed is in km/h but time is given in minutes, convert minutes to hours first (÷60).
(2) Clock conversion exceptions — 12:00 AM = 00:00 and 12:00 PM = 12:00 are the two special cases most students get wrong.
(3) Leap year century rule — divisible by 4 is not enough for century years. They need to be divisible by 400.
Quick MCQ Revision
| Formula | Remember |
|---|---|
Speed | Distance ÷ Time |
Distance | Speed × Time |
Time | Distance ÷ Speed |
1 hour | 60 min = 3600 sec |
Leap year | Divisible by 4 (century years: ÷ 400) |
PM → 24hr | Add 12 (except 12 PM stays 12:00) |
12 AM | = 00:00 (midnight) |