Time (Cambridge (CIE) IGCSE International Maths)

Time

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