Time (Copy)

Time Calculations Cheat Sheet (IGCSE Mathematics 0580)

1. Time Unit Conversions and Relationships

• 1 minute = 60 seconds
• 1 hour = 60 minutes
• 1 day = 24 hours
• 1 week = 7 days
• 1 year = 365 days (leap year = 366 days)
• 1 month ≈ 30 or 31 days (February = 28 or 29 days)
• 1 year = 12 months
• 1 decade = 10 years
• 1 century = 100 years

2. 12-Hour and 24-Hour Clock Conversions

• To convert 12-hour to 24-hour:
  • a.m.: Keep the time same, remove “a.m.”
  • p.m.: Add 12 to the hour (except 12 p.m. = 1200)
• To convert 24-hour to 12-hour:
  • 0000–1159 → Add “a.m.” (e.g., 0315 = 3:15 a.m.)
  • 1200–2359 → Subtract 12 and add “p.m.” (e.g., 1745 = 5:45 p.m.)

3. Reading Clocks and Timetables

• Analog Clock:
  • Short hand = Hour
  • Long hand = Minutes
  • 1 hour = 5 minute intervals on clock face
• Digital Clock:
  • 12-hour format includes a.m./p.m.
  • 24-hour format shows time in 4-digit notation
• Reading Timetables:
  • Match the departure and arrival times
  • Always check if time is in 12-hour or 24-hour format
  • Subtract times to find duration
    • Convert both to minutes or use time subtraction

4. Time Difference & Time Zones

• Time Zones:
  • World is divided into 24 time zones (1 hour per 15° longitude)
  • Time zones ahead are denoted as UTC+ (e.g., Pakistan is UTC+5)
  • Time zones behind are denoted as UTC− (e.g., New York is UTC−5)
• Time Difference Calculations:
  • Add or subtract time zone differences
  • Adjust across midnight if needed

Example:

• If it is 1600 hrs in London (UTC+0), what time is it in Karachi (UTC+5)?
  → 1600 + 5 hours = 2100 hrs (9:00 p.m.)

5. Working with Time Durations

• Subtracting time:
  • Borrow minutes if necessary
  • Example: 3:45 − 2:50 → Convert to minutes: 225 − 170 = 55 mins
• Adding time:
  • Add hours and minutes separately
  • Adjust if minutes ≥ 60

Example:

• Start: 10:50
• Add: 2 hr 30 min
  → 10:50 + 2:30 = 13:20 or 1:20 p.m.

6. Practical Applications

• Speed-Time-Distance Problems:
  • Speed = Distance ÷ Time
  • Ensure consistent units (convert minutes to hours etc.)
• Work Schedules / Shift Calculations
  • Include breaks where necessary
  • Calculate total working hours
• Exam Questions May Include:
  • Finding arrival/departure times
  • Converting between clock formats
  • Calculating durations from schedules
  • Working across different time zones

Tips

• Always convert all times to the same format before doing calculations.
• Use 24-hour format for clarity and avoiding confusion with a.m./p.m.
• In exam time questions, be careful with crossing midnight or working across days.