Time — Grade 3 Mathematics
In Grade 3, we learn to use the 24-hour clock, convert between 12-hour and 24-hour formats, calculate duration across midnight, and read simple timetables.
12-Hour vs 24-Hour Clock
The 12-hour clock uses AM/PM and numbers 1–12.
The 24-hour clock runs from 00:00 (midnight) to 23:59 and needs no AM/PM.
Converting:
AM times: add a leading zero (8:30 AM → 08:30)
PM times (except noon): add 12 to the hours (6:45 PM → 18:45)
Noon: 12:00 PM → 12:00 | Midnight: 12:00 AM → 00:00
The 24-hour clock runs from 00:00 (midnight) to 23:59 and needs no AM/PM.
Converting:
AM times: add a leading zero (8:30 AM → 08:30)
PM times (except noon): add 12 to the hours (6:45 PM → 18:45)
Noon: 12:00 PM → 12:00 | Midnight: 12:00 AM → 00:00
| 12-hour | 24-hour | Description |
|---|---|---|
| 12:00 AM | 00:00 | Midnight |
| 6:30 AM | 06:30 | Morning |
| 12:00 PM | 12:00 | Noon |
| 3:15 PM | 15:15 | Afternoon |
| 8:45 PM | 20:45 | Evening |
| 11:59 PM | 23:59 | Just before midnight |
Reading Timetables
| Station | Train A | Train B | Train C |
|---|---|---|---|
| City | 07:00 | 09:30 | 14:15 |
| Park Road | 07:22 | 09:52 | 14:37 |
| Market St | 07:45 | 10:15 | 15:00 |
| Airport | 08:10 | 10:40 | 15:25 |
Train A takes: 08:10 − 07:00 = 1 hour 10 minutes from City to Airport.
Worked Examples
Example 1 — Converting 12↔24 Hour
Convert: (a) 4:20 PM to 24-hour (b) 22:35 to 12-hour
- (a) PM: 4 + 12 = 16 → 16:20
- (b) 22 − 12 = 10 → 10:35 PM
Example 2 — Duration Across PM Hours
A bus leaves at 14:35 and arrives at 17:10. How long is the journey?
- 14:35 → 17:35 = 3 hours
- 17:35 → 17:10 = minus 25 minutes
- Actually: 17:10 − 14:35 = 2h 35min
- Method: 14:35 + 25 min = 15:00; 15:00 → 17:00 = 2h; 17:00 → 17:10 = 10 min
- Total = 25 min + 2h + 10 min = 2 hours 35 minutes
Example 3 — Real World: Using the Timetable 🚂
Using the timetable above, how long does Train C take from City to Market St?
- Departs City: 14:15 | Arrives Market St: 15:00
- Duration = 15:00 − 14:15 = 45 minutes
Practice Questions
1. Convert 7:45 PM to 24-hour clock.
✅ 7 + 12 = 19 → 19:45
2. Convert 13:20 to 12-hour clock.
✅ 13 − 12 = 1 → 1:20 PM
3. A film starts at 20:10 and ends at 22:25. How long is the film?
✅ 22:25 − 20:10 = 2 hours 15 minutes
4. Using the timetable above, how long does Train B take from Park Road to Airport?
✅ 09:52 → 10:40 = 48 minutes
5. How many minutes are in 3 hours 25 minutes?
✅ (3 × 60) + 25 = 180 + 25 = 205 minutes
Key Points to Remember
- 24-hour clock runs 00:00 to 23:59 — no AM/PM needed.
- PM → 24-hour: add 12 (except 12 PM stays 12:00).
- 24-hour → PM: subtract 12 (for times 13:00–23:59).
- To find duration: count up from start time to end time in stages.
- Timetables: read rows (stations) and columns (train/bus services) carefully.