CIE IGCSE Maths

Revision Notes

1.11.1 Time

What do I need to know about time for IGCSE?

  • Both 12-hour and 24-hour times could be used
  • In the 12-hour clock system …
    • AM is between midnight (12am) and midday (12pm)
    • PM is between midday (12pm) and midnight (12am)
  • Times may have to be read from both analogue and digital clocks
  • Times may have to be read from timetables

Time Notes fig1 (1), downloadable IGCSE & GCSE Maths revision notes Time Notes fig1 (2), downloadable IGCSE & GCSE Maths revision notes

  • Time does not work like the rest of the number system (based on 10s, 100s, etc) so calculations can get awkward
    • 60 seconds in a minute
    • 24 hours in a day
    • … and many more !

 

Time Notes fig2 (1), downloadable IGCSE & GCSE Maths revision notes Time Notes fig2 (2), downloadable IGCSE & GCSE Maths revision notes

How do I read a clock?

  • A 12-hour clock goes round once for am and once for pm
    • am is midnight (12am) to midday (12pm)
    • pm is midday (12pm) to midnight (12am)
  • A 24-hour clock uses four digits – two for the hour, two for the minutes
    • 1134 is 11.34am
    • The day starts at midnight which is 0000
    • 1pm is 1300, 2pm is 1400, … 10pm is 2200, 11pm is 2300

 

Time Notes fig3, downloadable IGCSE & GCSE Maths revision notes

  • Analogue clocks work in 12-hour time
  • On the minute hand each number is worth five minutes
    • Some clocks will have markings for individual minutes
  • The hour hand is always moving
    • At “half past” the hour hand should be halfway between two numbers

 

Time Notes fig4, downloadable IGCSE & GCSE Maths revision notes

  • Digital clocks can use either 24 hour time or 12-hour time
    • A “:” is often displayed between the hours and minutes
      eg 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
    • For single-digit hours, clocks often miss out the first zero
      eg 09:23 would be displayed as 9:23
  • Timetables (for a bus or train for example) use the 24‑hour time
    • Times are listed as four digits without the “:”

 

Time Notes fig5, downloadable IGCSE & GCSE Maths revision notes

How do I calculate with time in terms of the 12-hour clock?

  • Work in chunks of time
    • eg 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
    • Remember midday is 12pm and midnight is 12am

 

Time Notes fig6, downloadable IGCSE & GCSE Maths revision notes

How do I calculate with time in terms of the 24-hour clock?

  • Work in chunks of time just like the 12 hour clock calculations
    • eg. 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

 

Time Notes fig7, downloadable IGCSE & GCSE Maths revision notes

How do I use bus and train timetables?

  • These tend to use the 24-hour clock system
  • Each column represents a different bus/train – these are often called “services”
    • eg “The 0810 service from London King’s Cross”
  • The time in each cell usually indicate departure times (when the bus/train leaves that stop/station)
    • The last location on the list usually shows the arrival time

 

Time Notes fig8 (1), downloadable IGCSE & GCSE Maths revision notes Time Notes fig8 (2), downloadable IGCSE & GCSE Maths revision notes

Exam Tip

Even when allowed, put that calculator away for time-based questions, they are pretty useless for these calculations!

Worked Example

Time Example sol abc (q1), downloadable IGCSE & GCSE Maths revision notes Time Example sol abc (q2), downloadable IGCSE & GCSE Maths revision notes

Time Example sol abc (1), downloadable IGCSE & GCSE Maths revision notes Time Example sol abc (2), downloadable IGCSE & GCSE Maths revision notes Time Example sol d, downloadable IGCSE & GCSE Maths revision notes

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