1. UNITS OF TIME

2. Units of Time
YEAR
WEEK
MONTH
MINUTE
HOUR
SECOND
DAY

3. Units of Time
1 year = 365 days
1 year = 12 months
1 year = 52 weeks
1 week = 7 days
1 day = 24 hours
1 hour = 60 minutes
1 minute = 60 seconds

4. Time Definitions
a.m. or A.M. – an abbreviation of ante meridiem (before noon)
p.m. or P.M. – an abbreviation of post meridiem (after noon)

5. Time Definitions
International Date Line an imaginary line through the Pacific Ocean roughly along the 180th meridian, agreed upon as the place where each new calendar day begins. The calendar day to the east of the line is one day earlier than to the west.

6. Time Definitions
prime meridian – The zero meridian (0°) used as a reference line from which longitude east and west is measured. It passes through Greenwich, England.

7. Time Conversion
Using a bridge map can help organize your thinking when converting from one time unit to another.

8. Bridge Map as
(just like)
Relating factor

9. Time Conversion
Example:
4 weeks = ______ days 28
Think: 1 week = 7 days
4 x 7 = 28
1 week
4 weeks
7 days
___days 28

10. Time Conversion
Example: 36
3 years = ______ months
Think: 1 year = 12 months
3 x 12 = 36
1 year
3 years
12 months
___ months 36

11. Time Conversion
Example: 80
3 days 8 hours = ______ hours
Think: 1 day = 24 hours
3 x 24 = = 80
1 day
3 days 8 hours
24 hours
___ hours 80

12. Time Conversion
Example: 7
420 seconds = ______ minutes
Think: 60 seconds = 1 minute
420 ÷ 60 = 7
60 seconds
420 seconds
1 minute
___minutes 7

13. Time Conversion
Example: 3 6
42 months = __ years __ months
Think: 12 months = 1 year
42 ÷ 12 = 3 r 6
12 months
42 months
1 year
__ years __months 3 6

14. Time Conversion
Example:
4 1/6
100 hours = _____ days
Think: 24 hours = 1 day
100 ÷ 24 = 4 4/24 = 4 1/6
24 hours
100 hours
1 day
___ days
4 1/6

15. Time units can be added, subtracted, multiplied or divided.
Elapsed Time
Time units can be added, subtracted, multiplied or divided.
To add or subtract measures of time:
1. Add or subtract the seconds.
2. Add or subtract the minutes.
3. Add or subtract the hours.
Rename if necessary in each step.

16. Elapsed Time
Add minutes
Find the sum.
Add hours
15 h 23 min
+ 7 h 15 min
Rename answer if necessary
22 h
38 min

17. Elapsed Time
Add minutes
Find the sum.
Add hours
6 h 12 min
+ 1 h 55 min
Rename answer if necessary
67 min = 1 h 7 min
7 h
67 min
= 8 h 7 min

18. Elapsed Time
Find the difference.
Subtract minutes
Subtract hours
5 h 48 min
- 2 h 12 min
Rename answer if necessary
3 h
36 min

19. Rename answer if necessary
Elapsed Time
Find the difference.
Subtract seconds 23 5 10
Subtract minutes
24 min
min 12 s
60 s
Rename answer if necessary
10 min
48 s

20. Elapsed Time
To calculate elapsed time – subtract the starting time from the ending time of the event.
Ending Time
Starting Time
Elapsed Time
9:55 a.m.
6:35 a.m.
3 h 20 min

21. Elapsed Time
Marcy was babysitting from 7:30 p.m. to 10:50 p.m. How long did Marcy baby-sit?
Start time
Ending time
Subtract minutes
10:50
- 7:30
Subtract hours 3 hr 20
min
3 hours 20 minutes

22. Military time is based on a 24 hour clock.
Hours from 1:00 a.m. to 12:00 p.m are from 01:00 to 12:00
Hours from 1:00 p.m. to 12:00 a.m. are from 13:00 to 24:00

23. Military Time
Add 12 hours to 1: 00 p.m. to 12:00 a.m. to change from standard time to military time.
Examples:
1:30 a.m. is
01:30 military time
1:15 p.m. is
13:15 military time
9:45 p.m. is
21:45 military time
12:00 a.m. is
24:00 military time

24. Elapsed Time
Susie worked from 6:50 a.m. to 11:30 a.m. on Monday. How long did she work? 10 90
11:30
- 6:50
Rename 1 hour to minutes
Subtract minutes
Subtract hours 4 hr 40
min
4 hours 40 minutes

25. Elapsed Time
John worked from 1:45 p.m. to 8:25 p.m. on Wednesday. How long did he work? 7 85
Rename 1 hour to minutes
8:25
- 1:45
Subtract minutes
Subtract hours 6 hr 40
min
6 hours 40 minutes

26. Think:military time add 12 to hour
Elapsed Time
John worked from 10:30 a.m. to 6:00 p.m. on Friday. How long did he work?
Think:military time add 12 to hour 17 60
Add 12 to hour
18:00
6:00
- 10:30
Rename 1 hour to minutes
Subtract minutes
Subtract hours 7 hr 30
min
7 hours 30 minutes

27. Units of Time
Time units can be expressed using fractions..
Quarter of an hour
Half an hour