Time — Class 4 IMO

12-hour & 24-hour Clock

The 12-hour clock uses a.m. (before noon) and p.m. (after noon). The 24-hour clock counts the hours from 0 to 23, so afternoon times keep going: 1 p.m. is 13:00 and 8 p.m. is 20:00.

To change a p.m. time to 24-hour, add 12 to the hours. Midnight is 00:00 and noon is 12:00.

Example 1: Write 3 p.m. in 24-hour time.

3 + 12 = 15, so 15:00.

Example 2: Write 20:00 in 12-hour time.

20 − 12 = 8, so 8 p.m.

Quick recap

p.m. to 24-hour: add 12 to the hours.
Midnight = 00:00; noon = 12:00.

✓ Quick check

6 p.m. in 24-hour time is ___ ?

6 + 12 = 18, so 18:00.

14:00 in 12-hour time is ___ ?

14 − 12 = 2, so 2 p.m.

Converting Units & Finding Duration

There are 60 minutes in an hour and 60 seconds in a minute. To change hours to minutes, multiply by 60; to change minutes to seconds, multiply by 60.

To find a duration, add the interval to the start time: 9:00 + 2 hours 30 minutes = 11:30.

Example 1: Change 3 hours into minutes.

3 × 60 = 180 minutes.

Example 2: A bus leaves at 9:00 and travels for 2 hours 30 minutes. When does it arrive?

9:00 + 2 h 30 min = 11:30.

Quick recap

1 hour = 60 minutes; 1 minute = 60 seconds.
End time = start time + duration.

✓ Quick check

5 hours = ___ minutes?

5 × 60 = 300 minutes.

4 minutes = ___ seconds?

4 × 60 = 240 seconds.

Calendars & Timetables

A calendar helps us find the day for a date and count the days between two dates. From 10 March to 15 March is 5 days.

A timetable lists start and end times. The journey length is the end time minus the start time.

Example 1: How many days are there from 10 March to 15 March?

15 − 10 = 5 days.

Example 2: A train leaves at 9:00 and arrives at 11:30. How long is the journey?

11:30 − 9:00 = 2 hours 30 minutes.

Quick recap

Days between dates = later date − earlier date.
Journey time = arrival time − departure time.

✓ Quick check

How many days are there from 1 January to 8 January?

8 − 1 = 7 days.

A class runs from 10:00 to 10:45. How long is it?

From 10:00 to 10:45 is 45 minutes.