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Measuring Elapsed Time
Units of Time
• 1 minute (min) = 60 seconds (s)• 1 hour (h) = 60 minutes• 1 day = 24 h• 1 week (wk) = 7 days• 1 year is about 365 days• 1 year is about 52 weeks
Add or Subtract
3 h 15 min 52 sec1 h 42 min 11sec+
5 h 5min 29 sec3 h 15 min 52 sec
_
63 sec_60 sec
Elapsed time
• The time between two events is called elapsed time.
• If both times are AM, or both times are PM, then just subtract the times.
• Be careful when times pass midnight or noon.
Example: Find the elapsed time between 1:45 PM and 5:27 PM
5:27 5 h 27 min1:45 1 h 45 min
41 h = 60 min
87
3 h 42 min
How long is a school day that goes from 8:15 AM to 3:25 PM?When one time is in the morning, and one is in the afternoon, add 12 hours to the end-time. This takes care of passing from AM to PM.
3 hours 25 min 15 hours 25 min 8 hours 15 min
7 hours 10 min
Counting Up
Another way to deal with elapsed time that includes both AM and PM is to “count up.” Add hours and minutes at the end.
Example: How much time is between 5:45 AM and 7:20 PM?
5:45 to 6:00 15 min
6:00 to 12:00 6 h
12:00 to 7:00 7 h
7:00 to 7:20 20 min
Combine minutes with minutes: 15 + 20 = 35 minCombine hours with hours: 6 + 7 = 13 h
Answer: 13 hours and 35 minutes.