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
- The long hand is the hour hand
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
- A colon ':' is often displayed between the hours and minutes
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
- When it is 7 am in Helsinki
Examiner Tip
- Be careful in the exam if calculators are allowed, as they can often cause problems in time-based questions!
- Remember that 1 hour 30 mins of time would be 1.5 hours on a calculator
Worked example
Find the time at which the film ends.
Work in chunks of time
Add the hour on
There are 60 minutes in an hour
Add on 25 minutes of the remaining 45 minutes to get to the next hour
Write your final answer using the type of clock used in the question (24-hour) unless otherwise stated
Work in chunks of time
Find the number of minutes until the next hour
Work in chunks of time
Find the number of minutes until the next hour
Be careful about the AM/PM boundary
3 hours 4 minutes
Coronation Street | 0750 | 0800 | 0816 |
Albert Square | 0818 | 0830 | 0849 |
Ramsey Street | 0825 | 0840 | 0903 |
Emmerdale Village | 0834 | 0852 | 0918 |
How long should the journey between Coronation Street and Ramsey street take on the 0800 bus?
Worked example
The time in Madrid is 7 hours ahead of the time in Chicago.
Mark takes a flight from Madrid to Chicago which lasts 9 hours and 45 minutes.
The flight leaves at 7:30 am Madrid time.
What will the local time be in Chicago when he arrives?
Work in Madrid time, and then change at the end
Add 9 hours 45 minutes on to 7:30 am to find the time Mark arrives in Chicago (in Madrid time)
07:30 + 9 h 45m = 16:30 + 45m = 17:15
17:15 is the time in Madrid, so find the time in Chicago
Madrid is 7 hours ahead of Chicago
Subtract 7 hours
17:15 - 7 hours = 10:15
10:15 am