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TIME 12 hour clock For the 12 hour clock, the important time is 12 noon, which is the meridian. Time is measured in two 12 hour cycles, which are either the 12 hours before 12 noon, which are am, or the 12 hours after 12 noon which are pm. am stands for ante meridian which means before 12 noon pm stands for post meridian which means after 12 noon 2am 5.45pm 12 noon 12 midnight 24 hour clock In the 24 hour clock, time is measured in one 24 hour cycle, starting from immediately after midnight. When the time is on the precise hour it is given in hundreds. 0200 hours is read as "oh two hundred hours" 1200 hours is read as "twelve hundred hours" 2400 hours is read as " twenty four hundred hours" When minutes are involved the number for the hours is given first, followed by the minute time. 1745 hours is read as "seventeen forty-five hours" 0312 hours is read as "oh three twelve hours" Comparative times Noon Midnight 12.01am 1.00am 12.00noon 12.01pm 12.00pm 0001hours 0100hours 1200hours 1201hours 2400hours 1 Updated Feb 2013 Converting between time systems Given the time on a 12 hour clock you need to be able to convert it for a 24 hour clock. For the hours between 1 and 12, just write them down, with a 0 in front of a single digit number, followed by the minutes. 1.32am 0132hours 11.45am 1145hours For the hour between midnight (12.00pm) and 1am, you need to write 00 for the hour, followed by the minute time. 12.17am 0017hours For the hours between 12 noon and midnight (12.00pm) you need to add on 12 hours to the given time, then convert as before. 3.30pm 1530hours 11.55pm 2355hours You also need to be able to convert from a 24 hour clock to a 12 hour clock. For the hours between 1 and 12, just write the hours down, without the 0 in front for the single digit numbers, followed by a point, then the minutes. 0525hours 5.25am 1057hours 10.57am For the hour between midnight (12.00pm) and 1am, you need to replace the 00 with 12. 0050hours 12.50am For the hours between 1200 hours (12 noon) and 2400 hours midnight), you need to subtract 1200, then convert as before. 1812hours 6.12pm 1235hours 12.35pm 2 Updated Feb 2013 (12 Time problems How many minutes from 7.30am to 12.45am? 7.30am to 12.00am (12 noon) = 4 hours 30 minutes 12.00 noon to 12.45am = 12 hours 45 minutes Total time = 17 hours 15 minutes Total time in minutes = (17 60) + 15 minutes = 1035 minutes. Write 5.3 minutes in minutes and seconds. 5 minutes + (0.3 60) seconds = 5 minutes 18 seconds Write 345 minutes in hours and minutes. 345 60 = 5 hours and 45 minutes left over = 5 hours 45 minutes How many seconds in 1.5 hours? There are 3600 seconds in 1 hour 1.5 3600 = 5400 seconds What fraction of an hour is 25 minutes? 25 5 of an hour 60 12 You also need to be able to calculate numbers of days in months and years and also know what years a particular century spans. How many days are there between 15th January and 2nd April in a leap year? There are 31 days in January, so 31 – 15 = 16 29 days in February in a leap year 31 days in March + 2 days in April Total = 16 + 29 + 31 + 2 = 78 days. 3 Updated Feb 2013 Remember that when centuries are named, e.g. fifteenth century, the name is given to the century which will end in the year 1499. So the fifteenth century spans the years 1400 to 1499. Time exercises 1. How many minutes from 11.40 a.m. to 12.35 a.m? 2. It is 10.36 p.m. What was the time 2 12 hours ago? 3. How many minutes in 1 34 hours? 4. How many seconds in 2 14 minutes? 5. Write 2.2 minutes in minutes and seconds 6. Write 280 seconds in minutes and seconds 7. What fraction of an hour is 50 minutes? 8. What percentage of 1 hour is 20 min? 9. What time is 50 minutes after 4.45 p.m.? 10. A bus arrived 46 mins late at 2.34 p.m.? What time was it due? 11. If I left home at 7.43 a.m. and arrived at 2.35 p.m., how long did my journey take? 12. I start work at 7.45 a.m. and leave at 4.30 p.m. How long am I at work? 13. How many hours from 4 p.m.Tuesday to 11 a.m.Thursday? 14. How many hours in 2 3 of a day 15. What time is 11 hours before 4.30 p.m.? 16. Write 5.45 p.m. in 24 hour notation 17. Write 3.20 a.m. in 24 hour notation 18. It is 18.30 hours. What will be the time in 6 hours 30 minutes? 19. It is 11.00 hours. What was the time 13 12 hours ago? 20. If I study 2.5 hours every day, how many hours do I study in a week? 21. How many days from 12 July to 19 September? 4 Updated Feb 2013 22. How many weeks in 3 4 of a year? 23. How many days in June, July and August altogether? 24. If I sleep on average 8 hours every day, a) how many hours do I sleep in a year b) what percentage of my time do I sleep? 25. I get paid every fortnight. How many pays in a year? 26. How many days from February 20 to March 20 in a leap year? 27. How many years in 3.2 centuries? 28. What period does the seventeenth century span? Time solutions 18) 01.00 hours 1) 12 hours 55 minutes 19) 21.30 hours 2) 8.06 pm 20) 17.5 hours 3) 105 minutes 21) 69 days 4) 135 seconds 22) 39 weeks 5) 2 minutes 12 seconds 23) 92 days 6) 4 minutes 40 seconds 1 5 7) 6 24) a) 2920 hours 25) 26 1 3 8) 33 % 26) 29 days 9) 5.35 pm 27) 320 years 10) 1.48 pm 28) 1600 to 1699 11) 6 hours 52 minutes 12) 8 hours 45 minutes 13) 43 hours 14) 16 hours 15) 5.30 am 16) 17.45 hours 17) 03.20 hours 5 Updated Feb 2013 b) 33 3 %