Finding Elapsed Time Using a Number Line (Under 1 Hour) | Math with Mr. J

Added: 2026-05-30

[00:00:00]Welcome to Math with Mr. J.

[00:00:04]In this video, I'm going to go through an example of finding elapsed time using a number line. Now, remember, elapsed time is the amount of time that passes from the start of an event to the end.

[00:00:19]Basically, elapsed time is how much time something takes. Let's jump into our example where we have Jaylen started working on his science homework at 5:10 p.m. He finished his science homework at 5:55 p.m. How long did it take Jaylen to finish his science homework? Now, when it comes to elapsed time, we'll always have a start time and end time and then the elapsed time. Depending on the situation, we may need to figure out the start time, end time, or elapsed time.

[00:00:56]For this example, we're given the start time, 5:10 p.m. We're also given the end time. So, 5:55 p.m. We need to figure out the elapsed time. How long it took Jaylen to finish his science homework. Let's use a number line to help us figure this out. We always put our start time on the left.

[00:01:24]So, 5:10 here and then the end time goes on the right. So, 5:55.

[00:01:32]The space between the start and end is the elapsed time. This is what we need to figure out. Now, there are different strategies and ways to think through these. So, I'll go through a couple of different ways for this example. Just remember, we're going to work from the start time to the end time to figure out the total elapsed time. The first way we'll do this is by counting up by 10 minutes until we reach our end time. So, we're going to make 10-minute jumps.

[00:02:04]Now, can we make 1-minute jumps or 5-minute jumps? So, counting up by 1 minute or 5 minutes? Sure, those will work. We can count up by whatever we would like. But, the bigger the jumps, the less jumps we will need to make. And that makes things simpler. I chose 10 minutes here because 10 is easy to work with. We can easily count up by 10s. So, starting from the start time, we're going to make 10-minute jumps. So, 10 minutes that brings us to 5:20.

[00:02:39]Another 10 minutes brings us to 5:30.

[00:02:44]Plus another 10 minutes brings us to 5:40.

[00:02:49]Another 10 minutes brings us to 5:50.

[00:02:54]Now, if we do another 10 minutes, that brings us to 6:00. And that's past our end time. So, that's too much. We only need 5 minutes here. So, let's make a 5-minute jump. And that brings us to our end time, 5:55.

[00:03:13]Now, we add our elapsed time up. We have 10 minutes plus 10 minutes plus 10 minutes plus 10 minutes plus 5 minutes.

[00:03:24]So, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 45 minutes. And that's our elapsed time. So, it took Jaylen 45 minutes to finish his homework. Now, let's clear that and think through this another way. Now, another strategy and way to think through these is to use either exact hours, so 6:00, 8:00, and so on, or using half past an hour, so 6:30, 7:30, 8:30, and so on.

[00:04:02]This can give us easier times to work with and set us up with some big jumps on the number line. And really, thinking about these different strategies helps our overall ability to work with and think about time. So, for example, if we start at 5:10, so our start time 5:10, and we go ahead 20 minutes, so do a 20-minute jump, that gets us to 5:30.

[00:04:30]So, we're looking at getting to 5:30 here, and we needed 20 minutes to do so.

[00:04:37]Now, how do we get from 5:30 to 5:55?

[00:04:42]Well, we need to add 25 minutes. We need to go ahead 25 minutes and make that jump. And that brings us to our end time of 5:55. So, we have 20 minutes plus 25 minutes. So, we have 20 minutes to get to 5:30 plus 25 more minutes to get to 5:55.

[00:05:08]20 minutes plus 25 minutes gives us that elapsed time of 45 minutes. So, we get 45 minutes that way, as well. So, there you have it. There's an example of finding elapsed time using a number line. Just remember, there are different strategies and ways to think through these. So, use what works best for you.

[00:05:31]And the more of these problems you work through, the better you'll get. I hope that helped.

[00:05:38]Thanks so much for watching.

[00:05:40]Until next time, peace.

[00:05:52]>> Mhm.