Time
O Level and IGCSE Mathematics Cheat Sheet – 1.15 Time
Time Units and Conversions
| Unit | Conversion |
|---|---|
| 1 min | 60 s |
| 1 h | 60 min |
| 1 day | 24 h |
| 1 week | 7 days |
| 1 year | 365 days (366 in leap year) |
| 1 year | 12 months |
- Converting hours ↔ minutes ↔ seconds
Example: 2 h 30 min = 2.5 h (30 ÷ 60 = 0.5 h)
Example: 3.25 h = 3 h + (0.25 × 60) min = 3 h 15 min
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24-Hour and 12-Hour Clock
- 12-hour clock: Uses am (midnight to before noon) and pm (noon to before midnight).
- 24-hour clock: Hours run from 0000 to 2359.
- Conversions:
- 3:15 am = 0315
- 3:15 pm = 1515
- 0000 = midnight, 1200 = noon
Reading Clocks and Timetables
- Read start time and end time carefully.
- Subtract to find time difference, converting hours/minutes as needed.
- Example: Start 09:20, End 13:45 → Difference = 4 h 25 min.
Time Zones and Local Times
- Earth rotates 360° in 24 h → 15° per hour.
- Time difference between zones = difference in longitude ÷ 15.
- If travelling east → local time increases.
- If travelling west → local time decreases.
- Example: London (GMT) 10:00, Dubai (+4 h) → Local time = 14:00.
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Mathematics Full Scale Course
Practical Problems
- Speed problems: Convert all time to same unit before calculation.
- Schedules: Account for overnight journeys and day changes.
- Flight example: Depart 2230 local, flight 8 h, arrive in a city +3 h ahead → Arrival = (2230 + 8 h) + 3 h = 0930 next day.
Exam Special Tips
- Always state units in final answers.
- Convert decimal hours to h & min format for clarity.
- Watch for am/pm changes in 12-hour clock questions.
- For time zones, adjust direction (east or west) correctly.
Common Mistakes & Confusions
- Forgetting that 0.5 h = 30 min, not 50 min.
- Mixing 12-hour and 24-hour times without converting.
- Incorrectly adjusting date when crossing midnight.
- Misinterpreting timetable times as durations.