Time Concepts — Grade 5 Mathematics
In Grade 5, we extend our time skills to complex elapsed time, fluent use of the 24-hour clock, and an introduction to international time zones.
Unit Conversions
| Units | Relationship | Example |
|---|---|---|
| Seconds ↔ Minutes | ÷60 / ×60 | 195 s = 3 min 15 s |
| Minutes ↔ Hours | ÷60 / ×60 | 2¾ h = 165 min |
| Hours ↔ Days | ÷24 / ×24 | 3 days = 72 h |
| 12-hr ↔ 24-hr | PM: add 12 (except 12 PM=12:00) | 3:45 pm → 15:45 |
Calculating Elapsed Time — Jump Method
A flight departs at 08:45 and lands at 14:20. How long is the flight?
Start
+15 min
+5 h
+20 min
Total: 15 min + 5 h + 20 min = 5 hours 35 minutes
International Time Zones
Time zones tell us the local time in different parts of the world. UTC (Coordinated Universal Time) is the reference.
| City | UTC Offset | When UTC is 12:00 |
|---|---|---|
| London (GMT) | UTC+0 | 12:00 |
| Dubai | UTC+4 | 16:00 |
| New York | UTC−5 | 07:00 |
| Tokyo | UTC+9 | 21:00 |
Worked Examples
Write 7:05 am and 9:47 pm in 24-hour format.
- 7:05 am → 07:05 (before noon, just add leading zero)
- 9:47 pm → 9 + 12 = 21 → 21:47
A night train departs at 22:35 and arrives at 06:10 the next morning. How long is the journey?
- 22:35 → 23:00: 25 min
- 23:00 → 06:00: 7 hours
- 06:00 → 06:10: 10 min
- Total: 7 hours 35 minutes
It is 15:30 in London (UTC+0). What time is it in Tokyo (UTC+9)?
- UTC time = 15:30
- Tokyo = UTC + 9 hours
- 15:30 + 9:00 = 00:30 (next day)
Practice Questions
1. Convert 14:55 to 12-hour (am/pm) format.
2. A journey starts at 10:40 and lasts 3 hours 45 minutes. What is the arrival time?
3. A film starts at 19:15 and lasts 2 hours 50 minutes. What time does it finish?
4. How many minutes are in 4 days?
5. It is 09:00 in New York (UTC−5). What is the UTC time, and what time is it in Dubai (UTC+4)?
Key Points to Remember
- 24-hour clock: pm hours → add 12 (except 12 pm = 12:00); am hours keep as-is (leading zero for 01–09).
- Elapsed time: break the journey into easy jumps (to the next full hour, then whole hours, then remaining minutes).
- For journeys crossing midnight, count up from the start time to midnight (00:00) then add the remaining time.
- Time zones: local time = UTC + offset; negative offsets are behind UTC.
- 1 day = 24 hours = 1 440 minutes = 86 400 seconds.