Units of time
Time is measured in seconds, minutes, hours, days and weeks. In daily life we often need to change one unit into another, for example when we plan a journey or a lesson. Remember these facts: 1 minute = 60 seconds, 1 hour = 60 minutes, 1 day = 24 hours and 1 week = 7 days. Knowing them well makes every time question easier.
Key idea
To change hours into minutes, multiply by 60. To change minutes into hours, divide by 60.
The 24-hour system
In the 24-hour system we write time with 4 digits. Morning times are the same, but after noon we add 12 to the hour. So 3:00 p.m. becomes 1500, and 8:30 p.m. becomes 2030.
Worked example
A film starts at 2:15 p.m. and ends at 4:00 p.m. How long is it? From 2:15 to 4:15 is 2 hours, but it ends at 4:00, which is 15 minutes earlier. So the film lasts 1 hour 45 minutes.
Remember
- 1 h = 60 min, 1 min = 60 s.
- After 12:00 noon, add 12 to write the 24-hour time.
- To find a duration, count on from the start time.