Time | Mathematics for GCSE/IGCSE - Year 11 PDF Download

What do I need to know about time for IGCSE?

• Both 12-hour and 24-hour times could be used
• In the 12-hour clock system:
  • AM is between midnight (12am) and midday (12pm)
  • PM is between midday (12pm) and midnight (12am)
• Times may have to be read from both analogue and digital clocks
  
• Times may have to be read from timetables
  
• Time operates differently from the base-10 number system, making calculations somewhat tricky.
  • 60 seconds in a minute
  • 60 minutes in an hour 
  • 24 hours in a day
  • 7 days in a week
  • 365 days in a year
  • ... and many more !

• Knowing the number of days in each calendar month is important, and the following poem might help you remember...
  

How do I read a clock?

• A 12-hour clock goes round once for am and once for pm:
  • AM: Midnight (12am) to Midday (12pm)
  • PM: Midday (12pm) to Midnight (12am)
• A 24-hour clock uses four digits - two for the hour, two for the minutes:
  • Example: 1134 is 11:34 am
  • The day starts at midnight (0000)
  • 1pm is 1300, 2pm is 1400, ..., 10pm is 2200, 11pm is 2300

• Analogue clocks operate in a 12-hour format.
• On an analogue clock's minute hand, each number represents five minutes. Some clocks may have markings for individual minutes.
• The hour hand on an analogue clock is continuously moving.
  • When it is "half past" the hour, the hour hand should be positioned midway between two numbers, with the minute hand pointing at the 6.

• Digital clocks can display time in either 24-hour format or 12-hour format.
  • A ":" is commonly used between the hours and minutes (e.g., 12:45).
• When using 24-hour time, "am" or "pm" does not need to be specified.
  • For single-digit hours, the leading zero is often omitted (e.g., 9:23).
• Timetables, such as those for buses or trains, typically utilize the 24-hour time format.
  • Times in timetables are listed as four digits without the ":" separator.

How do I calculate with time in terms of the 12-hour clock?

• Divide the time calculation into chunks: start by calculating the minutes until the next hour, then move on to whole hours, and finally calculate the remaining minutes until the final time.
• Understand when the 12-hour clock transitions between AM and PM. Remember, 12 PM is midday, and 12 AM is midnight.

How do I calculate with time in terms of the 24-hour clock?

• Break down time calculations into chunks similar to 12-hour clock methods.
  • For example, calculate the minutes remaining until the next hour, then the whole hours, and finally the minutes until the end time.
• If the hour exceeds 12, subtract 12 to determine the 12-hour PM time.

How do I use bus and train timetables?

• These tend to use the 24-hour clock system
• Each column represents a different bus/train - these are often called "services" (e.g., "The 0810 service from London King's Cross")
• The time in each cell usually indicates departure times (when the bus/train leaves that stop/station). The last location on the list usually shows the arrival time