Mathematics — Measurement

Subtopic: Time (for age 10 — Kenyan context)

Time helps us know when things happen. We use clocks and calendars to measure time. In Kenya, you may use times to know when school starts (e.g. 8:00 am), when a football match begins, or when the bus leaves.

1. Units of time

• Second (s) — a very short time.
• Minute (min) — 60 seconds = 1 minute.
• Hour (h) — 60 minutes = 1 hour.
• Day — 24 hours = 1 day.
• Week — 7 days = 1 week.
• Month — about 30 or 31 days (February is shorter).
• Year — 12 months = 1 year.

2. Reading clocks

Clocks have three important hands:

• Hour hand — short, shows the hour.
• Minute hand — long, shows minutes (points to numbers that count by 5).
• Second hand — very thin, moves every second.

3. Digital time and AM / PM

Digital clocks show hours and minutes like 8:00 or 3:15. We add AM (morning) or PM (afternoon/evening) to say the part of day:

• 8:00 AM — morning (e.g. school assembly)
• 1:00 PM — after noon (lunchtime)
• 7:30 PM — evening (study, family time)

Some timetables use the 24-hour clock: 14:00 = 2:00 PM, 06:30 = 6:30 AM.

4. How to convert

Use these simple steps:

• To change hours to minutes: multiply hours × 60. Example: 2 hours = 2 × 60 = 120 minutes.
• To change minutes to hours: divide minutes ÷ 60. Example: 90 minutes = 90 ÷ 60 = 1 hour 30 minutes.
• Add or subtract times by adding hours and minutes. If minutes ≥ 60, convert to hours.

5. Examples

1. How many minutes in 3 hours? 3 × 60 = 180 minutes.
2. School from 8:00 AM to 1:00 PM — how long is the school day? 1:00 PM is 13:00. 13:00 − 8:00 = 5 hours.
3. If a match lasts 1 hour 45 minutes and starts at 3:30 PM, what time does it end? 3:30 + 1:45 = 5:15 PM.

6. Practice questions

1. Convert 150 minutes into hours and minutes.
2. What is 2 hours 20 minutes + 1 hour 50 minutes? Give answer in hours and minutes.
3. Read the clock: If the minute hand is at 3 and the hour hand is at 4, what is the time?
4. A bus leaves at 07:15 and the trip is 2 hours 40 minutes. What time does it arrive?
5. Change 4:30 PM to 24-hour time.

7. Helpful tips for learners

• Remember: minute hand tells minutes (counts in 5s around the clock).
• When adding minutes, if result is 60 or more, change 60 minutes to 1 hour.
• Practice reading both analogue and digital clocks — both appear in school timetables and transport schedules.