1. Elapsed Time How Can We Calculate How Much Time Has Gone By? April 5, 2010

2. Basics About Time 60 seconds = 1 minute 60 minutes = 1 hour 24 hours = 1 day 12:00 pm = Noon 12:00 am = Midnight The clock is broken up into 5 minute intervals. –An interval is the space between two units.

3. What is elapsed time? Elapsed time is the amount of time that has passed between a start time and an end time. An example: –Between 9:00 am and 10:00 am, one hour has passed. –The elapsed time between 9:00 am and 10:00 am is 1 hour (60 minutes).

4. How Much Time Has Elapsed? Try computing the elapsed time between these two clocks: Start TimeEnd Time 11:15 am 1:15 pm

5. How Much Time Has Elapsed? Figure out how many hours have elapsed: 11:15 am+ 2 hours = 1:15 pm 2 hours has elapsed between 11:15 am and 1:15 pm.

6. How Much Time Has Elapsed? Take a look at the two clocks below. How much time has elapsed between the two clocks? Start Time End Time 10:10 am 11:30 am

7. How Much Time Has Elapsed? Ask yourself: “Has 1 Hour Passed?” Start Time + 1 hour 10:10 am 11:10 am Yes, at least 1 hour has passed between 10:10 am and the end time of 11:30 am.

8. How Much Time Has Elapsed? Now ask: “How much time is left to count?” Start Time + 1 hour + 20 minutes 11:10 am 11:30 am 1 hour and 20 minutes have elapsed between the start time and the end time.

9. What if the Start Time and End Time Don’t Fall on Easy Intervals? How much time has elapsed between the two times below? Start Time End Time 6:45 pm 2:39 am

10. What if the Start Time and End Time Don’t Fall on Easy Intervals? Start counting by the hours: Start Time + 7 hours 6:45 pm 1:45 am

11. What if the Start Time and End Time Don’t Fall on Easy Intervals? Then count by 15 minute intervals: Start Time + 7 hours+ three 15-minute intervals 1:45 am 2:30 am

12. What if the Start Time and End Time Don’t Fall on Easy Intervals? Finally, figure out how much time is left: Start Time + 7 hours + 45 minutes+ 9 minutes 2:30 am 2:39 am The elapsed time is 7 hours + 45 minutes + 9 minutes = 7 hours and 54 minutes.