The 24-hour clock 1
12-hour clock
24-hour clock
The hours go from 12 to
12 twice a day
The hours go from 0 to
23
You must use am or pm:
Time is always shown
as four digits
am is before noon
You don’t use am or pm
pm is after noon
Used in timetables,
mobiles and computers
The 24-hour clock 2
After 12 o’clock in the afternoon, the hours continue to 13.00 = 1pm,
14.00 = 2pm, 15.00 = 3pm, up to 23.00 = 11pm.
After 23, the hour goes to 00.00 = 12am then through 01.00 = 1am,
02.00 = 2am all the way to 23.00 = 11pm then 00.00 again.
Because all the hours have a different number, there is no need
to use am or pm.
For example there are two 4 o’clocks in a day:
one in the morning
4:00 am = 04:00
one in the afternoon
4:00 pm = 16:00
An easy way to change to 24-hour time is to add 12 onto the
hour. You only do this to the hours between 1pm and 11pm.
Midnight becomes 00:00.
The 24-hour clock 3
Fill in the 24-hour times on the scale below on your worksheet.
am
12-hour time
pm
00.00
12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
24-hour time
The 24-hour clock 4
When converting to 24-hour time you change the hours only.
12 hour
3.00am
8.15am
11.45am
2.35pm
5.20pm
11.38pm
12.55am
24 hour
03:00
08:15
11:45
14:35
17:20
23:38
00:55
Notice that you only add 12 onto the pm times.
The 24-hour clock 5
Change the following times from 12 hour into 24 hour.
1. 5am
2. 8am
3. 2.45am
4. 12.02am
5. 11.38am
6. 12.01pm
7. 1.29pm
8. 7pm
9. 10.45pm
10. 11.07pm
1. 05:00
2. 08:00
3. 02:45
4. 00:02
5. 11:38
6. 12:01
7. 13:29
8. 19:00
9. 22:45
10. 23:07
Now check your answers.
The 24-hour clock 6
To convert from 24 hour to 12 hour you do the opposite.
Take away 12 from the hours if it is 13 to 23.
Midnight changes from 00:00 to 12:00am.
Change the following times from 24 hour into 12 hour.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
04:00
07:00
09:45
00:20
11:02
12:56
16:22
20:20
21:21
22:18
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Now check your answers.
4am
7am
9.45am
12.20am
11.02am
12.56pm
4.22pm
8.20pm
9.21pm
10.18pm
Time intervals 1
To calculate time intervals, you need to count forward.
You might want to calculate time intervals for a variety of
reasons.
You might want to know how long a film lasts, how long a journey
is going to last, how long you are in each class for in school.
Can you think of any other reasons why you might want to
calculate a time interval?
To calculate the interval between 4.00am and 7.00am you count
Forward.
Start at 4 and count forward to 7 = 3 hours.
+
1
1
4
5
+
1
6
7
Time intervals 2
Find out how long there is between each of these times
1.
2.
3.
4.
5.
6.
7.
5.00pm and 8.00pm
11.00pm and 4.00am
3.30pm and 6.30pm
22:40 and 00:40
07:05 and 12:05
12:55 and 14:55
Time intervals 3
Find out how long there is between each of these times
1.
2.
3.
4.
5.
6.
7.
3.15pm and 5.15pm
9.05pm and 2.05am
7.15pm and 10.15pm
14:10 and 23:10
17:25 and 22:25
13:05 and 18:05
Time intervals 4
To find out how many minutes there are between two time intervals
and the times are in the same hour, take away the minutes.
For example:
4.05 to 4.45
45 – 5 = 40 minutes
The times are in the same hour, 4.
This means that you can take away the minutes to calculate the
time interval.
6.20 to 6.55
55 - 20 = 35 minutes
14:05 to 14:25
25 – 5 = 25 minutes
Time intervals 5
Find out how long there is between each of these times:
1.
2.
3.
4.
5.
6.
7.
5.05pm and 5.20pm
11.00pm and 11.45pm
3.30pm and 3.55pm
22:40 and 22:55
07:05 and 07:45
12:45 and 12:55
Time intervals 6
Calculating time intervals in minutes from one hour to the next
can be broken down into two steps.
Step 1 Count the minutes to the next hour
Step 2 Add on the minutes to the finish time
How long is it in minutes between:
3.50 pm and 4.25 pm
Step 1 10 minutes till 4 o’clock
Step 2 4.00 – 4.25 = 25 minutes
10
+25
35 minutes
How long is it in minutes between
6.25 pm and 7.15 pm
Step 1 35 minutes till 7 o’clock
Step 2 7.00 – 7.15 = 15 minutes
35
+15
50 minutes
Time intervals 7
Find out how long there is between each of these times:
1.
2.
3.
4.
5.
6.
7.
5.55pm and 6.20pm
11.35pm and 12.20pm
3.30pm and 4.05pm
22:40 and 23:15
07:10 and 08:05
12:45 and 13:35
Time intervals 8
Remember that there are 60 minutes in an hour.
If the time interval adds up to more than 60 minutes, change it
into hours and minutes.
How long is it in minutes between:
3.40 pm and 4.55 pm
Step 1 20 minutes till 4 o’clock
Step 2 4.00 – 4.55 = 55 minutes
75 minutes = 1 hour (60 minutes) and 15 minutes
20
+55
75 minutes
How long is it in minutes between:
6.25 pm and 7.45 pm
Step 1 35 minutes till 7 o’clock
Step 2 7.00 – 7.45 = 45 minutes
80 minutes = 1 hour (60 minutes) and 20 minutes
35
+ 45
80 minutes
Time intervals 9
Find out how long there is between each of these times:
1.
2.
3.
4.
5.
6.
7.
5.50pm and 6.55pm
11.35pm and 12.50pm
3.30pm and 4.45pm
22:40 and 23:55
07:10 and 08:45
12:45 and 13:55
Time intervals 10
To calculate time intervals between hours follow these steps.
4.15 pm to 7.25 pm.
45 minutes
+ 2 hours
4.15 pm to 5.00 pm
45
+ 25
70 minutes
5.00 pm to 7.00 pm
+ 25 minutes
7.00 pm to 7.25 pm
70 minutes = 1 hour (60 minutes) and 10 minutes
+ 2 hours = 3 hours 10 minutes
19.20 pm to 21.55 pm.
40 minutes
19.20 to 20.00
40
+ 55
95 minutes
+ 1 hour
20.00 to 21.00
+ 55 minutes
21.00 to 21.55
95 minutes = 1 hour (60 minutes) and 35 minutes
+ 1 hour = 2 hours 35 minutes
Time intervals 11
Find out how long there is between each of these times:
1.
2.
3.
4.
5.
6.
7.
5.50pm and 8.55pm
11.35pm and 6.50pm
3.30pm and 12.45pm
22:40 and 00:55
07:10 and 12:45
12:45 and 20:55
Time intervals 12
It is also very useful to be able to calculate time intervals in days,
weeks and months.
You may want to know how long it is until your birthday, or how long
it is until your holidays or Christmas.
Can you think of any other reasons why you might want to
calculate time intervals using a calendar?
Calendars 1
August
Monday
Tuesday
Wednesday
Thursday
Friday
31
Saturday
Sunday
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
You can calculate how many weeks and days there are between
two dates by counting down the column.
How many weeks is it between the 5th and the 26th? = 3 weeks
How many weeks and days is it between the 5th and the 30th?
= 3 weeks and 4 days
Calendars 2
January
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
1. How long is it between January 7th and 21st?
2. How long is it between January 1st and 29th?
3. How long is it between January 13th and 27th?
4. How long is it between January 19th and 26th?
5. How long is it between January 21st and 28th?
Calendars 3
April
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
1. How long is it between April 1st and 23rd?
2. How long is it between April 1st and 9th?
3. How long is it between April 4th and 27th?
4. How long is it between April 7th and 30th?
5. How long is it between April 10st and 22nd?
Time intervals between months 1
January
Mon
day
Tues
day
Wed
nesd
ay
February
Thur
sday
Frida
y
Satu
rday
Sund
ay
1
2
3
4
Mon
day
Tues
day
Wed
nesd
ay
Thur
sday
Frida
y
Satu
rday
Sund
ay
1
5
6
7
8
9
10
11
2
3
4
5
6
7
8
12
13
14
15
16
17
18
9
10
11
12
13
14
15
19
20
21
22
23
24
25
16
17
18
19
20
21
22
26
27
28
29
30
31
23
24
25
26
27
28
How long is it between January 15th and February 12th?
4 weeks (you don’t include the 15th)
How long is it between January 15th and February 14th?
4 weeks and 2 days
Time intervals between months 2
January
Mon
Tue
Wed
February
Thu
Fri
Sat
Sun
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Mon
Tue
Wed
Thu
Fri
Sat
Sun
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
How long is it between the following dates:
1. January 1st and February 23rd?
3. January 28th and February 13th?
2. January 21st and February 28th?
4. January 31st and February 28th?
Time intervals between months 3
January
Mon
Tue
Wed
February
Thu
Fri
Sat
Sun
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Mon
Tue
Wed
Thu
Fri
Sat
Sun
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
How long is it between the following dates:
1. January 11th and February 4th?
3. January 18th and February 27th?
2. January 26th and February 19th?
4. January 27th and February 24th?
Time intervals between months 4
January
Mon
Tue
Wed
February
Thu
Fri
Sat
Sun
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Mon
Tue
Wed
Thu
Fri
Sat
Sun
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
How long is it between the following dates:
1. January 4th and February 1st?
3. January 15th and February 23rd?
2. January 13th and February 2nd?
4. January 18th and February 1st?