60 seconds = 1 minute
60 minutes = 1 hour
24 hours = 1 day
7 days = 1 week
52 weeks = 1 year
365 days = normal year
366 days = leap year
Leap years are divisible by 4
Centuries are not leap years unless divisible by 400
January 31 days
February 28 days (29 in leap year)
March 31 days
April 30 days
May 31 days
June 30 days
July 31 days
August 31 days
September 30 days
October 31 days
November 30 days
December 31 days
12 hour clock times are written with
am to represent morning
and pm to represent afternoon.
A colon is used to separate minutes.
Examples
9 :30 am is half past nine in the morning.
9: 37 pm is 23 minutes to ten in the evening.
24 hour clock times are written with 2 digits to show hours
and a colon to separate minutes.
Examples
09 :30 is half past nine in the morning.
21: 37 is 23 minutes to ten in the evening.
Military usage of 24 hour clock times
drops the colon
and adds the word hrs.
Examples
09 30 hrs is half past nine in the morning.
21 37 hrs is 23 minutes to ten in the evening.
To convert from 12 hour clock times to 24 hour clock times,
Examples
9:30 am = 09:30 or 09 30 hrs
3.15 pm = 15:15 or 15 15 hrs
Examples
03:15 = 3:15 am
23:23 = 11:23 pm
11 27 hrs = 11:27 am
21 00 hrs = 9 pm
Time 

12 hour 

24 hour 
Military 
Midnight 
= 
00:00 
00 00 hrs 
1 am 

01:00 
01 00 hrs 
Midnight 

00:00 
00 00 hrs 
Do not use your calculator – unless you are using the Deg,Hour,Min function.
Otherwise, your answer will not be converted properly.
Examples
calculate the time difference between
a) 11:07 and 11:30 b) 11:07 and 12:00
examples
calculate the time difference between :
a) 11:07 and 11:30
b) 11:07 and 12:00
C) 09:45 and 17:38
Remember
4.1 hrs = 4 hours 6 minutes , not 4 hours 10 minutes.
Hours 
Minutes 
1 
60 
0.05 
3 
0.1 
6 
0.15 
9 
0.2 
12 
0.25 
15 
0.3 
18 
0.35 
21 
0.4 
24 
0.45 
27 
0.5 
30 
0.55 
33 
0.6 
36 
0.65 
39 
0.7 
42 
0.75 
45 
0.8 
48 
0.85 
51 
0.9 
54 
0.95 
57 