UNITS OF TIME

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UNITS OF TIME
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Units of Time
YEAR
WEEK
MONTH
MINUTE
HOUR
SECOND
DAY
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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
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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)
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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.
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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.
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Time Conversion

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

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Bridge Map
as
(just like)
Relating factor
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Time Conversion
Example
4 weeks ______ days
28
Think 1 week 7 days
4 x 7 28
1 week
4 weeks
7 days
___days
28
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Time Conversion
Example
36
3 years ______ months
Think 1 year 12 months
3 x 12 36
1 year
3 years
12 months
___ months
36
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Time Conversion
Example
80
3 days 8 hours ______ hours
Think 1 day 24 hours
3 x 24 72 8 80
1 day
3 days 8 hours
24 hours
___ hours
80
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Time Conversion
Example
7
420 seconds ______ minutes
Think 60 seconds 1 minute
420 60 7
60 seconds
420 seconds
1 minute
___minutes
7
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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
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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
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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.
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Elapsed Time
Add minutes
Find the sum.
Add hours
15 h 23 min 7 h 15 min
Rename answer if necessary
38 min
22 h
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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
67 min
7 h
8 h 7 min
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Elapsed Time
Find the difference.
Subtract minutes
Subtract hours
5 h 48 min - 2 h 12 min
Rename answer if necessary
36 min
3 h
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Elapsed Time
Find the difference.
Subtract seconds
23
5
10
Subtract minutes
24 min - 13 min 12 s
60 s
Rename answer if necessary
10 min
48 s
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Elapsed Time
To calculate elapsed time subtract the starting
time from the ending time of the event.

• Ending Time
• Starting Time
• Elapsed Time

• 955 a.m.
• 635 a.m.
• 3 h 20 min

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Elapsed Time
Start time
Marcy was babysitting from 730 p.m. to 1050
p.m. How long did Marcy baby-sit?
Ending time
Subtract minutes
1050 - 730
Subtract hours
20
hr
3
min
3 hours 20 minutes
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Military Time
24 hour clock
Military time is based on a 24 hour clock.
Hours from 100 a.m. to 1200 p.m are from 0100
to 1200
Hours from 100 p.m. to 1200 a.m. are from 1300
to 2400
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Military Time
Add 12 hours to 1 00 p.m. to 1200 a.m. to
change from standard time to military time.
Examples
130 a.m. is
0130 military time
115 p.m. is
1315 military time
945 p.m. is
2145 military time
1200 a.m. is
2400 military time
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Elapsed Time
Susie worked from 650 a.m. to 1130 a.m. on
Monday. How long did she work?
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90
Rename 1 hour to minutes
1130 - 650
Subtract minutes
Subtract hours
40
hr
4
min
4 hours 40 minutes
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Elapsed Time
John worked from 145 p.m. to 825 p.m. on
Wednesday. How long did he work?
7
85
Rename 1 hour to minutes
825 - 145
Subtract minutes
Subtract hours
40
hr
6
min
6 hours 40 minutes
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Elapsed Time
Thinkmilitary time add 12 to hour
John worked from 1030 a.m. to 600 p.m. on
Friday. How long did he work?
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60
Add 12 to hour
1800
600 - 1030
Rename 1 hour to minutes
Subtract minutes
Subtract hours
30
hr
7
min
7 hours 30 minutes
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Units of Time
Time units can be expressed using fractions..
Quarter of an hour
Half an hour