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Measure Elapsed Time
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What you will learn from this videoWhat you will learn
- We’ll learn about elapsed time.
- That we can use the number line to measure elapsed time to the nearest minute!
- And that we can use this knowledge to find out how long it takes to do things like attend sporting events, get ready for school, and watch a movie!
- Discussion Questions
Before Video
Evan put a sandwich in the oven when his clock showed the hour hand pointing between the 7 and the 8. The minute hand was pointing directly at the 6. What time did the sandwich go in the oven? How can you tell?ANSWERIt is 7:30. The hour hand tells you that it is after 7 o’clock, and not yet 8 o’clock. The minute hand tells you it is 30 minutes after 7:00, so it is 7:30.
Each number on the clock face stands for the hour of the day, but it also stands for 5-minute intervals. You can count by 5s to find how many minutes it is after an hour.
You can add the minutes. Even put the sandwich in at 30 minutes past 7. 10 more than 30 is 40. Evan takes his sandwich out of the oven at 7:40.
It was 4:00 p.m. You can subtract 1 hour from the hours of the time. 5 – 1 = 4.
60 minutes pass between 4:00 and 5:00 because it is one hour, and one hour is the same amount of time as 60 minutes. Half an hour passes between 5:00 and 5:30, because 30 minutes is the same amount of time as half an hour.
After Video
How can you find the elapsed time between 9:30 a.m. and noon, in hours? ANSWERNoon is the same as 12:00 p.m., so I can use a number line and hop 2 hours from 9:30 to 11:30, then another half hour to noon, for a total of 2 ½ hours.
Use a number line. Given the start time, you hop forward to add the elapsed time and find the end time. 4:00 plus half an hour is 4:30 p.m. Given the end time, you hop backward to subtract the elapsed time and find the start time. 5:00 minus half an hour is 4:30 p.m.
Jason must leave before the start of his lesson, so I need to hop backward on the number line to find out what time he should leave: 1:00 p.m.
You could jump one hour, then jump in 5-minute intervals, like on a clock, to find the end time. Or, you could jump two hours, then jump back 20 minutes, because 40 minutes is 20 minutes less than one hour.
Kari is not correct. Start at 7:40 and count forward 37 minutes on a number line to find 8:17 p.m. This is after Kari’s class starts, so she will be late.
- Vocabulary
- Elapsed time DEFINE
The amount of time that passes between a start time and an end time.
- O'clock DEFINE
Means ‘of the hour’ and is used to tell that the current time is exactly on a given hour.
- Number line DEFINE
A straight line that is used to show the relationship between values. Points on the line indicate the relative position of numbers or values.
- Hour DEFINE
A unit of time that is equal to 60 minutes.
- Half-hour DEFINE
A unit of time that is equal to 30 minutes, which is half as long as one hour.
- Minute DEFINE
A unit of time that is equal to 60 seconds. There are 60 minutes in one hour.
- Elapsed time DEFINE
- Reading Material
- Practice Word Problems
- Practice Number Problems
- Lesson Plan
- Teacher Guide