The 24-hour clock 1

1
The 24-hour clock 1
12-hour clock The hours go from 12 to 12 twice a
day You must use am or pm am is before
noon pm is after noon
24-hour clock The hours go from 0 to 23 Time is
always shown as four digits You dont use am or
pm Used in timetables, mobiles and computers
2
The 24-hour clock 2
After 12 oclock 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 oclocks in a day
one in the morning 400 am 0400
one in the afternoon 400 pm 1600
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 0000.
3
The 24-hour clock 3
Fill in the 24-hour times on the scale below on
your worksheet.
12-hour time
am
pm
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
00.00
24-hour time
4
The 24-hour clock 4
When converting to 24-hour time you change the
hours only.
Notice that you only add 12 onto the pm times.
5
The 24-hour clock 5
Change the following times from 12 hour into 24
hour.

1. 0500
2. 0800
3. 0245
4. 0002
5. 1138
6. 1201
7. 1329
8. 1900
9. 2245
10. 2307

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

Now check your answers.
6
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 0000 to 1200am.
Change the following times from 24 hour into 12
hour.

1. 4am
2. 7am
3. 9.45am
4. 12.20am
5. 11.02am
6. 12.56pm
7. 4.22pm
8. 8.20pm
9. 9.21pm
10. 10.18pm

1. 0400
2. 0700
3. 0945
4. 0020
5. 1102
6. 1256
7. 1622
8. 2020
9. 2121
10. 2218

Now check your answers.
7
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
1
4
5
6
7
8
Time intervals 2
Find out how long there is between each of these
times

1. 5.00pm and 8.00pm
2. 11.00pm and 4.00am
3. 3.30pm and 6.30pm
4. 2240 and 0040
5. 0705 and 1205
6. 1255 and 1455

9
Time intervals 3
Find out how long there is between each of these
times

1. 3.15pm and 5.15pm
2. 9.05pm and 2.05am
3. 7.15pm and 10.15pm
4. 1410 and 2310
5. 1725 and 2225
6. 1305 and 1805

10
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
1405 to 1425
25 5 25 minutes
11
Time intervals 5
Find out how long there is between each of these
times

1. 5.05pm and 5.20pm
2. 11.00pm and 11.45pm
3. 3.30pm and 3.55pm
4. 2240 and 2255
5. 0705 and 0745
6. 1245 and 1255

12
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
10
Step 1 10 minutes till 4 oclock Step 2 4.00
4.25 25 minutes
25 35 minutes
How long is it in minutes between 6.25 pm and
7.15 pm
35
Step 1 35 minutes till 7 oclock Step 2
7.00 7.15 15 minutes
15 50 minutes
13
Time intervals 7
Find out how long there is between each of these
times

1. 5.55pm and 6.20pm
2. 11.35pm and 12.20pm
3. 3.30pm and 4.05pm
4. 2240 and 2315
5. 0710 and 0805
6. 1245 and 1335

14
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 oclock Step 2 4.00
4.55 55 minutes
20
55 75 minutes
75 minutes 1 hour (60 minutes) and 15 minutes
How long is it in minutes between 6.25 pm and
7.45 pm
Step 1 35 minutes till 7 oclock Step 2
7.00 7.45 45 minutes
35
45 80 minutes
80 minutes 1 hour (60 minutes) and 20 minutes
15
Time intervals 9
Find out how long there is between each of these
times

1. 5.50pm and 6.55pm
2. 11.35pm and 12.50pm
3. 3.30pm and 4.45pm
4. 2240 and 2355
5. 0710 and 0845
6. 1245 and 1355

16
Time intervals 10
To calculate time intervals between hours follow
these steps.
4.15 pm to 7.25 pm.
45 minutes
4.15 pm to 5.00 pm
5.00 pm to 7.00 pm
7.00 pm to 7.25 pm
45 25 70 minutes
70 minutes 1 hour (60 minutes) and 10
minutes
2 hours 3 hours 10 minutes
19.20 pm to 21.55 pm.
55 minutes
40 minutes
1 hour
19.20 to 20.00
20.00 to 21.00
21.00 to 21.55
40 55 95 minutes
95 minutes 1 hour (60 minutes) and 35
minutes
1 hour 2 hours 35 minutes
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Time intervals 11
Find out how long there is between each of these
times

1. 5.50pm and 8.55pm
2. 11.35pm and 6.50pm
3. 3.30pm and 12.45pm
4. 2240 and 0055
5. 0710 and 1245
6. 1245 and 2055

18
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?
19
Calendars 1
August August August August August August August
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
31 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
20
Calendars 2
January January January January January January 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?
21
Calendars 3
April April April April April April 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?
22
Time intervals between months 1
January January January January January January 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
February February February February February February February
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
How long is it between January 15th and February
12th?
4 weeks (you dont include the 15th)
How long is it between January 15th and February
14th?
4 weeks and 2 days
23
Time intervals between months 2
January January January January January January January
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 29 30 31
February February February February February February February
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?
4. January 31st and February 28th?
2. January 21st and February 28th?
24
Time intervals between months 3
January January January January January January January
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 29 30 31
February February February February February February February
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?
4. January 27th and February 24th?
2. January 26th and February 19th?
25
Time intervals between months 4
January January January January January January January
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 29 30 31
February February February February February February February
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?
4. January 18th and February 1st?
2. January 13th and February 2nd?