Primary 3 maths · Measurement & time · About 10 minutes
Find start times, finish times and durations
Mark the known endpoints or gap. Cross hour boundaries in useful jumps.
Start the interactive lesson →Open practice activity
What you will learn
- Find start times, finish times and durations
Models used: number sentences, stories, tables.
Before you start
Jump to the next hour first
An activity starts at 9:45. We want to go forward by 30 minutes.
The dots are times of day. Each curved arrow is a number of minutes passing.
An activity starts at 9:45. We want to go forward by 30 minutes.
Split a long wait into easier jumps. Add the durations of the jumps, not the clock readings at their ends.
The dots are times of day. Each curved arrow is a number of minutes passing.
First use 15 minutes to reach 10 o’clock.
Split a long wait into easier jumps. Add the durations of the jumps, not the clock readings at their ends.
The dots are times of day. Each curved arrow is a number of minutes passing.
There are 15 minutes still to use. Another jump takes us to 10:15.
15 + 15 = 30 minutes
Split a long wait into easier jumps. Add the durations of the jumps, not the clock readings at their ends.
What did the picture help us see?
There are 15 minutes still to use. Another jump takes us to 10:15.
Worked example: A new example, together
An activity ends at 14:50 after 55 minutes. When did it start?
| Start | Duration | Finish |
|---|---|---|
| ? | 55 minutes | 14:50 |
A timeline relationship. Read each value with the heading above its column.
Mark the known endpoints or gap. Cross hour boundaries in useful jumps.
A duration is the time between the start and finish. Move forward from the start, or backwards from the finish, by that duration.
A timeline relationship Start Duration Finish ? 55 minutes 14:50 A timeline relationship. Read each value with the heading above its column.
Use the relationship: start time + duration = finish time.
A timeline relationship Start Duration Finish ? 55 minutes 14:50 An activity ends at 14:50 after 55 minutes. When did it start?
13:55
A timeline relationship. Read each value with the heading above its column.
Move backwards by the duration.
A timeline relationship Start Duration Finish ? 55 minutes 14:50 A timeline relationship. Read each value with the heading above its column.
13:55 + 55 minutes = 14:50.
A timeline relationship Start Duration Finish ? 55 minutes 14:50 A timeline relationship. Read each value with the heading above its column.
Check the result against the question we started with.
14:50 minus 55 minutes returns to 13:55.
We found 13:55. A duration is the time between the start and finish. Move forward from the start, or backwards from the finish, by that duration.
A timeline relationship Start Duration Finish ? 55 minutes 14:50
Common mistakes to discuss
- Writing a time past sixty. Count on to the next hour, then add what is left. 9:45 plus 30 minutes is 10:15, never 9:75.
Check your understanding
- Find start times, finish times and durations
- explain time calculations as movement along a timeline
- check the answer against the original quantities and units
Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.
Try this lesson →Related Primary 3 lessons
- Add and subtract money in decimal notationAdd and subtract money in decimal notation · About 10 minutes
- Measure length in kilometres and liquid volume in millilitresMeasure length in kilometres and liquid volume in millilitres · About 10 minutes
- Use compound measurement unitsUse compound measurement units · About 10 minutes
- Convert km and m; m and cm; kg and g; litres and mlConvert km and m; m and cm; kg and g; litres and ml · About 10 minutes
- Use seconds as a unit of timeUse seconds as a unit of time · About 10 minutes
- Read and use the 24-hour clockRead and use the 24-hour clock · About 10 minutes