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
Examiner Tip
- Even if allowed, put that calculator away for time-based questions!
- Remember that 1 hour 30 mins of time would be 1.5 hours on a calculator.
- It is usually as quick and as accurate to use non-calculator skills.
- There is a button/mode on most makes/models of calculator that can help but it takes some getting used to.
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
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
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
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
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
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