Syllabus Edition

First teaching 2023

First exams 2025

|

Time (CIE IGCSE Maths: Core)

Revision Note

Test yourself

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

Common time conversions

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

12-hour clocks and 24-hour clocks

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

Reading the time from an analogue clock

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

Reading the time from a digital clock

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

Calculations with the 12-hour clock

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

Calculations with the 24-hour clock

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

A bus timetable

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 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

(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

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Naomi C

Author: Naomi C

Expertise: Maths

Naomi graduated from Durham University in 2007 with a Masters degree in Civil Engineering. She has taught Mathematics in the UK, Malaysia and Switzerland covering GCSE, IGCSE, A-Level and IB. She particularly enjoys applying Mathematics to real life and endeavours to bring creativity to the content she creates.