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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

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The 24-hour clock 2 After 12 oclock in the afternoon, the hours continue to = 1pm, = 2pm, = 3pm, up to = 11pm. After 23, the hour goes to = 12am then through = 1am, = 2am all the way to = 11pm then 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: 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. one in the morning 4:00 am = 04:00 one in the afternoon 4:00 pm = 16:00

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The 24-hour clock 3 Fill in the 24-hour times on the scale below on your worksheet hour time am pm 24-hour time 00.00

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The 24-hour clock 4 When converting to 24-hour time you change the hours only. 12 hour24 hour 3.00am03: am08: am11: pm14: pm17: pm 23: am00:55 Notice that you only add 12 onto the pm times.

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The 24-hour clock 5 Change the following times from 12 hour into 24 hour. 1.5am 2.8am am am am pm pm 8.7pm pm pm 1.05: : : : : : : : : :07 Now check your answers.

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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. 1.04: : : : : : : : : :18 1.4am 2.7am am am am pm pm pm pm pm Now check your answers.

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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. 4 Start at 4 and count forward to 7 = 3 hours

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Time intervals 2 Find out how long there is between each of these times pm and 8.00pm pm and 4.00am pm and 6.30pm 4.22:40 and 00: :05 and 12: :55 and 14:55 7.

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Time intervals 3 Find out how long there is between each of these times pm and 5.15pm pm and 2.05am pm and 10.15pm 4.14:10 and 23: :25 and 22: :05 and 18:05 7.

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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 The times are in the same hour, 4. This means that you can take away the minutes to calculate the time interval. 45 – 5 = 40 minutes 6.20 to = 35 minutes 14:05 to 14:2525 – 5 = 25 minutes

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Time intervals 5 Find out how long there is between each of these times: pm and 5.20pm pm and 11.45pm pm and 3.55pm 4.22:40 and 22: :05 and 07: :45 and 12:55 7.

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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 oclock Step – 4.25 = 25 minutes How long is it in minutes between 6.25 pm and 7.15 pm Step 1 35 minutes till 7 oclock Step – 7.15 = 15 minutes minutes minutes

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Time intervals 7 Find out how long there is between each of these times: pm and 6.20pm pm and 12.20pm pm and 4.05pm 4.22:40 and 23: :10 and 08: :45 and 13:35 7.

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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 – 4.55 = 55 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 – 7.45 = 45 minutes 80 minutes = 1 hour (60 minutes) and 20 minutes minutes minutes

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Time intervals 9 Find out how long there is between each of these times: pm and 6.55pm pm and 12.50pm pm and 4.45pm 4.22:40 and 23: :10 and 08: :45 and 13:55 7.

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Time intervals 10 To calculate time intervals between hours follow these steps pm to 7.25 pm pm to 5.00 pm5.00 pm to 7.00 pm7.00 pm to 7.25 pm 45 minutes+ 2 hours+ 25 minutes + 2 hours = 3 hours 10 minutes pm to pm to to minutes+ 1 hour to minutes minutes minutes 70 minutes = 1 hour (60 minutes) and 10 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: pm and 8.55pm pm and 6.50pm pm and 12.45pm 4.22:40 and 00: :10 and 12: :45 and 20:55 7.

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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?

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Calendars 1 You can calculate how many weeks and days there are between two dates by counting down the column. August MondayTuesdayWednesdayThursdayFridaySaturdaySunday How many weeks is it between the 5 th and the 26 th ?= 3 weeks How many weeks and days is it between the 5 th and the 30 th ? = 3 weeks and 4 days

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January MondayTuesdayWednesdayThursdayFridaySaturdaySunday Calendars 2 1. How long is it between January 7 th and 21 st? 2. How long is it between January 1st and 29th? 3. How long is it between January 13 th and 27 th? 4. How long is it between January 19 th and 26 th ? 5. How long is it between January 21 st and 28 th?

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Calendars 3 1. How long is it between April 1 st and 23 rd ? 2. How long is it between April 1 st and 9 th? 3. How long is it between April 4 th and 27 th? 4. How long is it between April 7 th and 30 th ? 5. How long is it between April 10 st and 22 nd? April MondayTuesdayWednesdayThursdayFridaySaturdaySunday

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Time intervals between months 1 January Mon day Tues day Wed nesd ay Thur sday Frida y Satu rday Sund ay February Mon day Tues day Wed nesd ay Thur sday Frida y Satu rday Sund ay How long is it between January 15 th and February 12 th ? 4 weeks (you dont include the 15 th ) How long is it between January 15 th and February 14 th ? 4 weeks and 2 days

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Time intervals between months 2 January MonTueWedThuFriSatSun February MonTueWedThuFriSatSun How long is it between the following dates: 1. January 1 st and February 23 rd ? 2. January 21 st and February 28 th ? 3. January 28 th and February 13 th ? 4. January 31 st and February 28 th ?

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January MonTueWedThuFriSatSun February MonTueWedThuFriSatSun How long is it between the following dates: 1. January 11 th and February 4 th ? 2. January 26 th and February 19 th ? 3. January 18 th and February 27 th ? 4. January 27 th and February 24 th ? Time intervals between months 3

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January MonTueWedThuFriSatSun February MonTueWedThuFriSatSun How long is it between the following dates: 1. January 4 th and February 1 st ? 2. January 13 th and February 2 nd ? 3. January 15 th and February 23 rd ? 4. January 18 th and February 1 st ? Time intervals between months 4

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