Time (CIE IGCSE Maths: Core)

How do I convert between different units of time?

• Time has a number of different conversions and does not use the decimal number system (based on 10s, 100s, etc)
  • You need to know the follow time conversions

• • You should also know the number of days in each calendar month

What is the difference between a 12-hour clock and a 24-hour clock?

• A 12-hour clock goes around once for AM and once for PM in one complete day
  • AM is between midnight (12 am) and midday (12 pm)
  • PM is between midday (12 pm) and midnight (12 am)
• A 24-hour clock goes around once for one complete day
  • The display uses four digits, two for the hour, two for the minutes
  • The day starts at midnight which is 00 00 (12 am) and goes up to 23 59 (11.59 pm)
• You need to be able to read the time from both a 12-hour clock and a 24-hour clock

How do I read the time from an analogue clock?

• An analogue clock works in 12-hour time
  
  • The long hand is the hour hand
    • Each number on the clock represents one hour for the hour hand
  • The short hand is the minute hand
    • Each number on the clock represents five minutes for the minute hand
    • Some clocks will have markings for individual minutes

How do I read the time from a digital clock?

• A digital clock can use either 24 hour time or 12-hour time
  • A colon ':' is often displayed between the hours and minutes
    • E.g.,  1245 would be displayed as 12:45
  • AM or PM does not need to be specified with 24-hour time
    • it may or may not be shown on a 12-hour time digital clock
  • For single-digit hours, clocks often miss out the first zero
    • e.g.  09:23 would be displayed as 9:23

How do I calculate with time using the 12-hour clock?

• Work in chunks of time
  • Calculate the minutes until the next hour, then whole hours, then minutes until a final time
• Ensure you know when the 12-hour clock switches from AM to PM and vice versa

How do I calculate with time using the 24-hour clock?

• Work in chunks of time just like the 12-hour clock calculations
  • Calculate the minutes until the next hour, then whole hours, then minutes until a final time
• If the hour is greater than 12, subtract 12 from it to find the 12-hour PM hour

How do I use bus and train timetables?

• Bus and train timetables tend to use the 24-hour clock system
  
  • Each column represents a different bus or train
  • Times are listed as four digits without the colon ':'
  • The time in each cell usually indicates the departure time (when the bus/train leaves that stop/station)
  • The last location on the list usually shows the arrival time

How do I convert time between time zones?

• Different countries are in different time zones, depending on where they are on the planet
• For example when it is 11:36 in London in the UK, it may be 06:36 in New York in the USA
  • So New York is 5 hours behind London
  • London is 5 hours ahead of New York
• You must consider:
  • What is the time difference between the two locations (in hours)?
  • Which time zone is ahead, and which one is behind?
• For example, Buenos Aires (Argentina) is 6 hours behind Helsinki (Finland)
  • When it is 7 am in Helsinki
    • 7 am - 6 hours = 1 am in Buenos Aires
  • When it is 5 pm in Buenos Aires
    • 5 pm + 6 hours = 11 pm in Helsinki