Elapsed time is the length of time between a start and end time.
Let's say Abby is playing with her friends at the park.
When she started playing, it was 2:00 p.m.
She decided to head back home at 3:00 p.m.
How long did Abby play in the park?
She played for 1 hour.
We call this the elapsed time.
Let's look at three ways to find the elapsed time.
We can use a number line to find the elapsed time.
What interval should we use between the tick marks?
Interval means the difference between two tick marks.
Intervals of 1 hour works well for our problem.
Each interval is like a "step" that we take on the line.
How many "steps" do we need to take to go from 2:00 p.m. to 3:00 p.m.?
Correct, we only take 1 step.
One step means 1 hour.
So, we just used a number line to figure out that the elapsed time between 2:00 p.m. and 3:00 p.m. is 1 hour. ✅
John started driving to his office at 7:35 a.m. He got there at 7:55 a.m. How long did it take him to get to his office?
What interval should we use in our number line?
The start and end times are multiples of 5.
We'll try 10-minute intervals.
Now, let's plot the start and end times on the line.
Then, we count the steps from the start time to the end time.
There are 2 steps between the two times.
So, we multiply 10 minutes by 2.
10 minutes × 2 = 20 minutes
The elapsed time from 7:35 to 7:55 is 20 minutes. ✅
Tip: There is no single rule on what interval to use. The idea is to pick the interval that's easiest for you.
In the example above, you could also have picked 5 minutes as the interval.
It's easy to figure out elapsed time if the start and end times are exact multiples of 1 hour, 5 minutes or 10 minutes.
But what if the problem looks like this?
Betty started coloring the picture at 4:42 p.m. She finished at 5:03 p.m. How much time did it take for Betty to color the picture?
The minutes in these times don't seem to be multiples of each other.
If we use a number line, it's not easy to decide what interval to use.
Using 1 minute as an interval will mean too much work.
Instead of using a number line, let's convert the hours into minutes and subtract them.
How do we convert 5:03 into minutes?
We start with 5 hours.
1 hour is 60 minutes. 5 hours multiplied by 60 minutes is 300 minutes.
Then, we add the 3 minutes.
300 + 3 = 303 minutes
5:03 is equal to 303 minutes.
Next, let's convert 4:32 to minutes.
4 hours multiplied by 60 minutes is equal to 240 minutes.
Then we add 32 minutes.
240 + 32 = 272 minutes
We now have both times in minutes.
Finally, we can subtract to find the elapsed time.
303 minutes - 272 minutes = 31 minutes
We have our answer:
It took 31 minutes for Betty to color the picture. ✅
Zoom is a cool trick that will help you to easily remember how to figure out elapsed time.
Let's use this trick to solve this problem:
Maria is driving to her grandma's house. She left her house at 7:45 a.m. and arrived at 11:20 a.m. How long did it take for Maria to drive to her grandma's house?
First, we draw a large Z.
Imagine you're zooming from left to right.
Then top to bottom. And finally, from left to right. 🏂
We write the start time at the beginning of Z. Then we write the end time at the end of it.
First, write the next hour on the point opposite the start time.
Now, figure out how many minutes it took to round up to the next hour.
The next hour is 8:00 a.m.
It takes 15 minutes to go from 7:45 to 8:00.
Let's write it on the top line.
Now, what is the hour of the ending time?
The hour of the ending time is 11:00. We write that on the lower left side of Z.
The difference between 8:00 and 11:00 is 3 hours.
Write that in the diagonal line in the middle.
How many minutes would it take to get from the end hour to the end time?
The difference between 11:00 and 11:20 is 20 minutes.
Let's write that on the bottom line.
To find the elapsed time, add up all the times in the middle.
So let's add these times:
Our elapsed time is 3 hours and 35 minutes.
It took Maria 3 hours and 35 minutes to drive to her grandma's house. ✅
Great job. 🎉
Let's say the start time is 9:36 a.m. and the end time is 2:47 p.m.
What is the elapsed time?
There are different ways to solve this.
Let's use the number line first.
Tip: Draw as many 1-hour intervals as you can before going past your end time.
How many steps to get to 2:36 from 9:36?
5 steps.
Since each step is equal to 1 hour, that means 5 hours.
Now, we still have time left between 2:36 and 2:47.
Let's subtract. We can disregard the hour since both are 2.
47 minutes - 36 minutes = 11 minutes
We add 11 minutes to the 5 hours that we got before.
5 hours + 11 minutes = 5 hours and 11 minutes
The elapsed time between 9:36 a.m. and 2:47 p.m. is 5 hours and 11 minutes. ✅
Remember: Try to use the largest time interval to go from the start to the end time.
Now imagine this:
Mrs. Williams is puts a dish in the oven at 4:45 p.m. She needs to cook it for 1 hour and 15 minutes. What time will she take the dish out of the oven?
We start by drawing a number line. We know the start time.
We need to jump a total of 1 hour and 15 minutes from 4:45 p.m.
Doing one big jump can be tricky.
So let's take smaller steps.
🚶 We take a small 15-minute step from 4:45 to the next hour.
The next hour is 5:00 p.m.
Remember to subtract 15 minutes from our elapsed time.
We have 1 hour left.
Taking a big 1-hour jump from 5:00 p.m. is easy.
It will bring us to 6:00 p.m.
Do we still have any time left in our elapsed time?
None left. ❎
That means our end time is 6:00 p.m.
Mrs. Williams has to take the dish out of the oven at 6:00 p.m. ✅
Now, you're ready for the practice.