Stage 5 · Time & measures
The 24-hour clock
a.m. stays; p.m. hours add 12.
How to do it
Method
a.m. stays; p.m. hours add 12
3 p.m.: 3 + 12 = 15 → 15:00
Another way
A time line
On a time line, 3 p.m. lines up with 15:00
In full
Morning times stay as they are: 9 a.m. is 9:00 (written 09:00). Afternoon hours gain 12: 3 p.m. → 3 + 12 = 15 → 15:00. Back the other way, 13:00 to 23:00 lose 12 to give the p.m. hour: 18:00 → 18 − 12 = 6 → 6 p.m. You can also line a.m., p.m. and the 24-hour clock up on a time line or a 24-hour clock face; the answer is the same.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
3 p.m. = ?:00
Show the answer and working
Answer: 3 p.m. = 15:00
3 p.m.: afternoon hours gain 12, 3 + 12 = 15 → 15:00
Example 2
3 a.m. = ?:00
Show the answer and working
Answer: 3 a.m. = 3:00
3 a.m.: morning times stay as they are, no 12 added → 3:00 (written 03:00)
Example 3
1 a.m. = ?:00
Show the answer and working
Answer: 1 a.m. = 1:00
1 a.m.: morning times stay as they are, no 12 added → 1:00 (written 01:00)
Example 4
17:00 = ? p.m.
Show the answer and working
Answer: 17:00 = 5 p.m.
17:00: 13:00 to 23:00 lose 12 to give the p.m. hour, 17 − 12 = 5 → 5 p.m.
Practise the 24-hour clock in the game →Stage 5 · Time & measures · Free to start, unlimited questions, no download