Grade 4 Mathematics Measurement – Time Notes

Mathematics — Measurement: Time

These notes explain the idea of time for a 9-year-old learner (Kenyan context). You will learn units of time, how to read clocks (digital and analogue), how to change one unit to another, and how to work out elapsed time.

1. What is time?

Time tells us when things happen. We use clocks and calendars to know the time and date.

2. Units of time

• 1 minute = 60 seconds
• 1 hour = 60 minutes
• 1 day = 24 hours
• 1 week = 7 days
• 1 month = about 30 days (some have 31, February has 28 or 29)
• 1 year = 12 months = 365 days (or 366 days in a leap year)

3. Reading clocks

We read clocks in two main ways:

• Digital clock: looks like 08:15 or 3:30
• Analogue (face) clock: has hour hand (short) and minute hand (long)

4. Words for common clock times

• Quarter past = 15 minutes past (e.g., 9:15)
• Half past = 30 minutes past (e.g., 2:30)
• Quarter to = 15 minutes to the next hour (e.g., quarter to 5 = 4:45)
• O'clock = exact hour (e.g., 6:00 = six o'clock)

5. AM and PM

The 12-hour clock uses AM and PM.
- AM: from midnight (12:00 AM) to just before noon (11:59 AM). Morning time.
- PM: from noon (12:00 PM) to just before midnight (11:59 PM). Afternoon, evening, and night.
Example: School starts at 8:00 AM; the school day may end at 3:30 PM.

6. Converting minutes and hours

To change hours to minutes, multiply by 60. To change minutes to hours, divide by 60.

7. Elapsed time (how long between two times)

To find elapsed time:

1. Write the start time and the finish time.
2. Count hours first, then count minutes.
3. Or change both times to minutes and subtract.

8. Kenyan daily examples

• School starts: 8:00 AM
• Break time: 10:15 AM (quarter past ten)
• Lunch: 1:00 PM
• School ends: 3:30 PM (half past three)
• Match starts at 4:45 PM (quarter to five)

9. Quick practice (try these)

1. Write these in words: 6:00, 2:15, 9:30, 11:45.
2. If a lesson starts at 9:45 and lasts 40 minutes, what time does it finish?
3. Convert: 3 hours = ? minutes. 150 minutes = ? hours and minutes.
4. A bus leaves Nairobi at 7:20 AM and arrives at 10:50 AM. How long is the trip?

10. Tips for learning time

• Practice reading both analogue and digital clocks every day.
• Use a real clock to move hands to show different times.
• Use calendar practice to learn days, weeks and months (e.g., name months in Kiswahili/English).
• When converting, remember 60 minutes in one hour and 24 hours in one day.