The idea, step by step
Jump to a landmark
Elapsed time is how long an event lasts. From 9:45 to 10:20, jump 15 minutes to 10:00, then 20 minutes to 10:20. The total is 35 minutes. Counting across an hour avoids treating a clock like a base-ten number line.
Choose the direction
If the start and duration are given, count forwards to the finish. If the finish and duration are given, count backwards to the start. Keep track of noon or midnight when you cross them. Check that your answer fits the part of the day and the length of the activity.
| Event | Time |
|---|---|
| Reading begins | 9:10 am |
| Reading ends | 9:45 am |
| Recess begins | 10:40 am |
A common trap
Subtracting clock digits as ordinary decimal numbers.
Instead: An hour contains 60 minutes. Use clock jumps or convert the whole duration into minutes.
See the thinking
Across an hour
A swim runs from 10:35 am to 11:15 am. Find its duration.
- 10:35 to 11:00 is 25 minutes.
- 11:00 to 11:15 is 15 minutes.
- 25 + 15 = 40 minutes.
Working backwards
A 50-minute club ends at 4:20 pm. Find its start time.
- Move back 20 minutes to 4:00 pm.
- There are another 30 minutes to move back.
- 4:00 pm minus 30 minutes is 3:30 pm.
Check your understanding
A film begins at 2:45 pm and lasts 30 minutes. When does it finish?
Show answer
3:15 pm.
15 minutes reaches 3:00 pm, then another 15 reaches 3:15 pm.
Your turn
6 questions · 8 marks · Work at your own pace.
Read the questions online
- A lesson runs from 9:15 am to 9:50 am. Find its duration.1 mark
- A walk runs from 11:40 am to 12:10 pm. Find its duration.1 mark
- A game starts at 3:25 pm and lasts 45 minutes. Find the finish time.1 mark
- A bus arrives at 5:05 pm after a 30-minute trip. Find its departure time.1 mark
- A trip starts at 8:50 am and ends at 10:15 am. Find its duration.2 marks
- Ella must arrive by 2:00 pm. Her walk takes 25 minutes. What is the latest time she can leave?2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- A lesson runs from 9:15 am to 9:50 am. Find its duration.1 mark
50 − 15 = 35 minutes.
35 minutes. - A walk runs from 11:40 am to 12:10 pm. Find its duration.1 mark
20 minutes to noon plus 10 minutes after noon gives 30.
30 minutes. - A game starts at 3:25 pm and lasts 45 minutes. Find the finish time.1 mark
35 minutes reaches 4:00 pm, then another 10 reaches 4:10 pm.
4:10 pm. - A bus arrives at 5:05 pm after a 30-minute trip. Find its departure time.1 mark
Back 5 minutes to 5:00 pm, then back 25 to 4:35 pm.
4:35 pm. - A trip starts at 8:50 am and ends at 10:15 am. Find its duration.2 marks
10 minutes to 9:00, then 60 to 10:00, then 15 more.
85 minutes equals 1 hour 25 minutes.
1 hour 25 minutes. - Ella must arrive by 2:00 pm. Her walk takes 25 minutes. What is the latest time she can leave?2 marks
Count backwards 25 minutes from 2:00 pm.
1:35 pm.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum Mathematics 2026
am/pm; unit conversions; start/finish/elapsed time.
Official curriculum source ↗