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2

3

1 year = 365 days

1 year = 52 weeks1 year = 12 months

1 week = 7 days1 day = 24 hours1 hour = 60 minutes1 minute = 60 seconds

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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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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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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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as(just like)

Relating factor

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Example:4 weeks = ______ days28

Think: 1 week = 7 days

4 x 7 = 28

1 week7 days

4 weeks ___days28

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Example:3 years = ______ months

3 x 12 = 36

36

Think: 1 year = 12 months

1 year12 months

3 years ___ months36

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Example:3 days 8 hours = ______ hours

3 x 24 = 72 + 8 = 80

80

Think: 1 day = 24 hours

1 day24 hours

3 days 8 hours ___ hours80

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Example:420 seconds = ______ minutes

420 ÷ 60 = 7

7

Think: 60 seconds = 1 minute

60 seconds1 minute

420 seconds ___minutes7

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Example:42 months = __ years __ months

Think: 12 months = 1 year

42 ÷ 12 = 3 r 6

3 6

12 months1 year

42 months __ years __months3 6

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Example:100 hours = _____ days

Think: 24 hours = 1 day

100 ÷ 24 = 4 4/24 = 4 1/6

4 1/6

24 hours1 day

100 hours ___ days4 1/6

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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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Find the sum. 15 h 23 min

+ 7 h 15 min

Add minutes

38 min

Add hours

22 h

Rename answer if necessary

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Find the sum. 6 h 12 min

+ 1 h 55 min

Add minutes

67 min

Add hours

7 h

Rename answer if necessary

= 8 h 7 min

67 min = 1 h 7 min

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Find the difference. 5 h 48 min

- 2 h 12 min

36 min

Subtract hours

3 h

Subtract minutes

Rename answer if necessary

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Find the difference. 24 min

- 13 min 12 s

Subtract minutes

10 min

Subtract seconds

Rename answer if necessary

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60 s

48 s

5 10

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Ending Time

- Starting Time

Elapsed Time

To calculate elapsed time – subtract the starting time from the ending time of the event.

9:55 a.m.

- 6:35 a.m.

3 h 20 min

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10:50

- 7:30

Subtract minutes

20hr

Subtract hours

33 hours 20 minutes

Start timeEnding time

Marcy was babysitting from 7:30 p.m. to 10:50 p.m. How long did Marcy baby-sit?

min

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Military time is based on a 24 hour clock.

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

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Add 12 hours to 1: 00 p.m. to 12:00 a.m. to change from standard time to military time.

Examples:

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

1:30 a.m. is 01:30 military time

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11:30

- 6:50

40hr4

Susie worked from 6:50 a.m. to 11:30 a.m. on Monday. How long did she work?

10 90

Subtract hoursSubtract minutesRename 1 hour to minutes

4 hours 40 minutesmin

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8:25

- 1:4540hr

John worked from 1:45 p.m. to 8:25 p.m. on Wednesday. How long did he work?

7 85

Subtract hoursSubtract minutes

Rename 1 hour to minutes

6 hours 40 minutes6 min

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6:00

- 10:30

30hr7

Think:military time

add 12 to hour

John worked from 10:30 a.m. to 6:00 p.m. on Friday. How long did he work?

Add 12 to hour

7 hours 30 minutes

18:0017 60

Rename 1 hour to minutes

Subtract hoursSubtract minutes

min

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Time units can be expressed using fractions..

Quarter of an hour

Half an hour