Time — Grade 4 Mathematics
In Grade 4, we convert between seconds, minutes, hours, days, and weeks, calculate elapsed time across the hour, and use both 12-hour and 24-hour clocks to solve timetable problems.
Time Conversions
Key facts:
• 60 seconds = 1 minute • 60 minutes = 1 hour • 24 hours = 1 day
• 7 days = 1 week • 365 days = 1 year (366 in a leap year)
• 60 seconds = 1 minute • 60 minutes = 1 hour • 24 hours = 1 day
• 7 days = 1 week • 365 days = 1 year (366 in a leap year)
| To convert | Operation | Example |
|---|---|---|
| minutes → seconds | × 60 | 5 min = 300 s |
| seconds → minutes | ÷ 60 | 180 s = 3 min |
| hours → minutes | × 60 | 2.5 h = 150 min |
| minutes → hours | ÷ 60 | 90 min = 1 h 30 min |
Calculating Elapsed Time
Use the jump method: jump to the next convenient hour or half-hour, then count the rest.
Example: From 10:45 to 13:20
10:45 → 11:00 = 15 min 11:00 → 13:00 = 2 h 13:00 → 13:20 = 20 min
Total = 2 h 35 min
Example: From 10:45 to 13:20
10:45 → 11:00 = 15 min 11:00 → 13:00 = 2 h 13:00 → 13:20 = 20 min
Total = 2 h 35 min
10:45
Start
11:00
+15 min
13:00
+2 h
13:20
+20 min
Worked Examples
Example 1 — Convert Hours and Minutes
Express 3 hours 25 minutes in minutes.
- 3 hours = 3 × 60 = 180 minutes
- 180 + 25 = 205 minutes
Example 2 — Find End Time
A film starts at 14:35 and lasts 1 hour 48 minutes. When does it end?
- 14:35 + 1 hour = 15:35
- 15:35 + 48 min: 35 + 48 = 83 min = 1 h 23 min
- 15:35 + 48 min = 16:23
Example 3 — Timetable Problem 🚂
A train departs at 09:47 and arrives at 12:15. How long is the journey?
- 09:47 → 10:00 = 13 min
- 10:00 → 12:00 = 2 h
- 12:00 → 12:15 = 15 min
- Total = 2 h + 13 min + 15 min = 2 h 28 min
Practice Questions
1. Convert 4 minutes 30 seconds to seconds.
✅ 4 × 60 + 30 = 270 seconds
2. Express 150 minutes in hours and minutes.
✅ 150 ÷ 60 = 2 remainder 30 → 2 hours 30 minutes
3. How many minutes are in 3 hours 45 minutes?
✅ 3 × 60 + 45 = 225 minutes
4. A lesson starts at 11:20 and ends at 12:05. How long is the lesson?
✅ 11:20 → 12:00 = 40 min; 12:00 → 12:05 = 5 min; total = 45 minutes
5. A race begins at 08:55 and takes 2 hours 37 minutes. What time does it finish?
✅ 08:55 + 2 h = 10:55; 10:55 + 37 min = 11:32 → 11:32
Key Points to Remember
- 60 seconds = 1 minute; 60 minutes = 1 hour; 24 hours = 1 day.
- Use the jump method to find elapsed time: jump to the next hour first.
- 24-hour clock: 14:00 = 2 pm; midnight = 00:00; noon = 12:00.
- To find end time: add hours first, then add the remaining minutes.
- Always check: if minutes exceed 60, carry 1 hour and subtract 60 from minutes.