Elapsed Time

1. Elapsed Time Open Number Line

2. Open Number Line Strategies for Addition

3. Addition – Student 1 • 36 + 24 +4 +10 +10 36 60 46 56 36 + 24 = 60

4. Addition – Student 2 • 36 + 24 +10 +10 +4 36 60 40 50 36 + 24 = 60

5. Addition – Student 3 • 36 + 24 +20 +4 36 60 56 36 + 24 = 60

6. Open Number Line Strategies for Subtraction

7. Subtraction – Student 1 • 53 - 37 Strategy: count up from the smallest number +3 +3 +10 10 + 3 + 3 = 16 37 53 47 50 53 - 37 = 16

8. Subtraction – Student 2 • 53 - 37 Strategy: count back from the largest number -3 -10 -3 3 + 3 + 10 = 16 37 53 40 43 53 - 37 = 16

9. Subtraction – Student 3 • 53 - 37 Strategy: count back from the largest number -3 -10 -10 -4 -10 16 53 20 33 43 23 53 - 37 = 16

10. Elapsed Time Using Benchmarks

11. How long is the movie? • I started watching a movie at 3:30 pm and it ended at 4:45 pm.

12. Elapsed Time • The movie started at 3:30 and ended at 4:45. How long was the movie? +30 min +30 min +15 min Strategy: Start at 3:30 and add time increments to the hour or ½ hour, (benchmarks), then continue until end time. 3:30 4:45 4:00 4:30 30 + 30 + 15 = 75 minutes = 1 hour 15 minutes

13. How much time is there between school and bedtime? • How much time is there between the time school is out (3:40 pm) and bedtime (8:15 pm)?

14. Elapsed Time – using benchmarks • How much time is there between 3:40 and 8:15? Strategy: Start at 3:40 and add time increments to the ½ hour benchmarks, then continue increments. +20 min +4 hours +15 min 3:40 8:15 4:00 8:00 4 hours + 20 min. + 15 min.= 4 hours 35 minutes

15. Time over the 12:00 hour • How much time is there between 10:30 am and 2:45 pm?

16. Elapsed Time – over 12 o’clock hour • How much time is there between 10:30 am and 2:45 pm? +30 min. +1 hour +2 hours +45 min Strategy: Add increments to 12:00, then continue benchmark increments. 2:45 2:00 11:00 12:00 noon 10:30 1 hr. + 2 hr. + 30 min. + 45 min. = 3 hr. 75 min. = 4 hr. 15 min.

17. Find the ending time • What time is 4 hours and 30 minutes from 6:55?

18. Finding the ending time – Student 1 • What time is it 4 hours and 30 minutes from 6:55? Strategy: Add minute increments to the ½ hour benchmark, then hours, then minutes. +4 hr. +5 min +25 min 11:00 11:25 7:00 6:55 The time is11:25, which is 4 hrs. and 30 min. after 6:55.

19. Finding the ending time – Student 2 • What time is it 4 hours and 30 minutes from 6:55? Strategy: Add hour increments until close, then minutes to the ½ hour, then minutes. +1 hr. +1 hr. +1 hr. +1 hr. +5 min +25min 11:00 11:25 7:55 8:55 10:55 6:55 9:55 The time is11:25, which is 4 hrs. and 30 min. after 6:55.

20. Find the start time • What time did we start on our trip if we arrived at 8:17 and it took 3 hours and 10 minutes?

21. Finding the start time • What time did we start on our trip if we arrived at 8:17 and it took 3 hours and 10 minutes? -10 min. -3 hr. Strategy: Subtract the hours then minutes. 8:17 5:07 5:17 The start time is 5:07.

22. Find the start time • What time do I need to wake up if I have to be at school at 8:15 am and it takes me 1 hour and 45 minutes to get ready?

23. Finding the start time • What time do I need to wake up if I have to be at school at 8:15 am and it takes me 1 hour and 45 minutes to get ready? -1 hr. -15 min. -15 min. -15 min. Strategy: Subtract the hour, then minute benchmarks. 8:15 6:30 6:45 7:00 7:15 I have to wake up at 6:30 AM.