🔢 MathGrade 3Lesson 22
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Calculate Elapsed Time

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Learning Objectives

  • 1Calculate elapsed time in hours and minutes
  • 2Find start or end time given a duration
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Mini Lesson

Elapsed time is the amount of time that passes between a start time and an end time. To find elapsed time, count on from the start time to the end time. You can count hours first, then minutes, or use a number line timeline.

Method: Count On

  1. Start at the given start time.
  2. Count on in hours until you reach or pass the end time.
  3. Then count on in minutes to reach the exact end time.
  4. Add the hours and minutes together for the total elapsed time.
Example

Train leaves at 9:30, arrives at 11:00. What is the elapsed time?

Answer:1 hour 30 minutes. From 9:30, add 1 hour to get 10:30, then add 30 more minutes to get 11:00.

Finding Start or End Time

  • To find end time: start time + duration = end time.
  • To find start time: end time - duration = start time.
  • Example: Film ends at 4:30, lasts 1 hour 30 min. Start = 4:30 - 1:30 = 3:00.
Elapsed time timeline: day camp 8:00 to 15:00A number line timeline from 8:00 to 15:00 with an arc labeled 7 hours above.Elapsed Time Timeline8:009:0010:0011:0012:0013:0014:0015:007 hoursStartEndDay camp: 8:00 to 15:00 = 7 hours
Step-by-step elapsed time: 9:30 to 11:00Two-step diagram showing Start 9:30 plus 1 hour gives 10:30, then plus 30 minutes gives End 11:00.Step-by-Step Elapsed TimeStart9:30+1 hr10:30+30 minEnd11:001 hr + 30 min = 1 hour 30 minutesTrain journey: 9:30 to 11:00
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Use a timeline or number line to visualize elapsed time. Mark the start, count on in hours, then add extra minutes.

Vocabulary
Elapsed time
The amount of time that passed between a start and ende.g. From 9:30 to 11:00 the elapsed time is 1 hour 30 minutes.
Start time
When something beginse.g. My lesson start time is 8:00.
End time
When something finishese.g. The end time of the show was 4:15.
Duration
How long something takese.g. The movie has a duration of 90 minutes.
Number line
A line that helps you count time forward in jumpse.g. I used a number line to add 30 minutes.
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← Lesson 21: Tell Time to the MinuteLesson 23: Measure Perimeter of Polygons →