Time (Cambridge (CIE) IGCSE International Maths)
Revision Note
Written by: Naomi C
Reviewed by: Dan Finlay
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
Examiner Tips and Tricks
Be careful when using a calculator, 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
You can use the degrees, minutes and seconds function to enter time on your calculator
E.g. 3 minutes 45 seconds would be entered as
You can convert between an answer on the calculator, given in either format of time, by pressing this button
Worked Example
(a) A film starts at 15 35 and lasts for 1 hour 45 minutes.
Find the time at which the film ends.
Work in chunks of time
Add the hour on
15 35 + 1 hour = 16 35
Add on the number of minutes until the next hour
There are 60 minutes in an hour
Add on 25 minutes of the remaining 45 minutes to get to the next hour
16 35 + 25 minutes = 17 00
There are 45 - 25 = 20 minutes left of the film to add
Write your final answer using the type of clock used in the question (24-hour) unless otherwise stated
17 25
(b) It is due to start raining at 02 35 and not stop until 08 14.
Find the time, in hours and minutes, it is expected to rain for.
Work in chunks of time
Find the number of minutes until the next hour
02 35 + 25 minutes = 03 00
Find the number of hours until the hour in the stopping time
03 00 + 5 hours = 08 00
Find the remaining minutes until the rain stops
08 00 + 14 minutes = 08 14
Add together the hours and minutes
25 minutes + 5 hours + 14 minutes
5 hours 39 minutes
(c) A train journey started at 11.23 am and finished at 2.27 pm.
How long, in hours and minutes, was the train journey?
Work in chunks of time
Find the number of minutes until the next hour
Be careful about the AM/PM boundary
11.23 am + 37 minutes = 12.00 pm
Add on the number of hours until the hour in the arrival time
12.00 pm + 2 hours = 2.00 pm
Add on the remaining minutes until the arrival time
2.00 + 27 minutes = 2.27 pm
Add up the hours and minutes to find the total length of the train journey
37 minutes + 2 hours + 27 minutes
37 minutes + 27 minutes add up to 1 hour and 4 minutes
3 hours 4 minutes
(d) The table below shows part of a bus timetable.
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?
The 08 00 bus is the middle column
Find the time between the departure times at Coronation Street and Ramsey street for the middle column
08 40 - 08 00
40 minutes
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
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