6.3 Calculate time difference
You may need to work out differences in time, e.g. to work out the length of a TV programme or journey time.
There are different ways to work out the difference in time. One of the easiest ways is to use the adding on method.
Example: Time difference by adding on
How long is it from 08:45 to 10:30?
Method
The start time is 08:45.
The number of minutes between 08:45 and the start of the next hour, 09:00, is 15 minutes.
The number of hours between 09:00 and 10:00 is one hour.
The number of minutes between 10:00 and 10:30 is 30 minutes.
So the time between 08:45 to 10:30 is:
15 minutes + 30 minutes + 1 hour = 1 hour 45 minutes
Now try the following activity.
Activity 23: Time difference
What is the length of time between the following times?
- 03:55 to 06:35
- 09:45 to 12:15
- 08:26 to 10:14
- 7:55 a.m. to 1:10 p.m.
- Midday to 15:50
- 3:15 am to midnight
Answer
-
The start time is 03:55.
The number of minutes between 03:55 and the start of the next hour, 04:00, is 5 minutes.
The number of hours between 04:00 and 06:00 is two hours.
The number of minutes between 06:00 and 06:35 is 35 minutes.
So the time between 03:55 to 06:35 is:
- 5 minutes + 35 minutes + 2 hours = 2 hours 40 minutes
-
The start time is 09:45.
The number of minutes between 09:45 and the start of the next hour, 10:00, is 15 minutes.
The number of hours between 10:00 and 12:00 is two hours.
The number of minutes between 12:00 and 12:15 is 15 minutes.
So the time between 09:45 to 12:15 is:
- 15 minutes + 15 minutes + 2 hours = 2 hours 30 minutes
Following the same method, you should have these answers for the other questions:
- 1 hour 48 minutes
- 5 hours 15 minutes
- 3 hours 50 minutes
- 20 hours 45 minutes
You should now be feeling comfortable with calculations involving time and timetables. Before you move on to looking at problems that involve average speed, it is worth taking a brief look at time conversions. Since you are already confident with converting units of measure, this part will just consist of a brief activity so that you can practice converting units of time.