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.