00:00Hey guys, today I'm in the clock classroom to solve some problems.
00:07I already know how to tell time, but now I want to learn about how I can add and subtract time.
00:13Come on over to my board with me.
00:18Here we are at the chalkboard looking at a number line.
00:21You might wonder why we are looking at a number line when we are going to work on problems involving time.
00:27Well, a number line can be used to help us understand what is being represented in the problem.
00:34This simple number line has the numbers 1, 2, and 3.
00:38We can say that each one of these numbers represents an hour.
00:44You should already know that an hour is made up of 60 minutes.
00:48When we go from 1 o'clock to 2 o'clock, 60 minutes or one hour has passed.
00:55We can also break down the hour into smaller segments.
00:59It would take forever to draw 60 small lines in between each of these hours, so we will not use individual minutes.
01:06We can, however, start at half hours or 30 minutes.
01:12These lines represent 30 minute intervals or half hours.
01:16We can also break it down further into 15 minute or quarter hour segments as well.
01:23With this number line, we can now see visually how time has passed.
01:27For example, let's say I started playing games at 1.15 PM.
01:32I finished playing games at 2.30 PM.
01:36How long did I play games?
01:39By counting the amount of time from the start to the end on the number line, we will know how long I played games.
01:46One easy way to work this problem is to make jumps by the hour.
01:50So we start at 1.15 and jump one hour.
01:54And that takes us to 2.15.
01:57We now have jumped one hour, but we are still not quite there yet.
02:01We need to make one more jump.
02:03How many more minutes do we need to jump to make it to 2.30?
02:07We need to jump 15 more minutes.
02:11So the total amount we jumped was one hour and 15 minutes.
02:17Great job, guys!
02:18This is awesome!
02:20We just used a number line to solve a time problem.
02:24Let's bring in a word problem and see how the number line helps us.
02:31Here is a word problem that says Katie started eating her lollipop at 1.15 PM, but didn't finish until 3.43 PM.
02:39How long did it take her to finish her lollipop?
02:42That must have been a huge lollipop!
02:46This problem can seem tricky, but once we start using the number line, we will figure it out.
02:51We start at 1.15 and move up an hour to 2.15.
02:58Looks like we can still move another hour, so let's do that.
03:03From 2.15 to 3.15 is another hour.
03:07We have moved 2 hours and that got us to 3.15, but she did not finish until 3.43.
03:14We need to figure out how many minutes are between 3.15 and 3.43.
03:20To do this, we are going to jump in smaller increments.
03:24We can go from the 15 here and jump 15 minutes.
03:29We are now at 3.30.
03:31If we jump another 15 minutes, where does that put us?
03:36We actually jumped past where we need to be.
03:39We are now at 3.45.
03:41Let's erase this jump so we can learn how to make smaller jumps.
03:46We are back to 3.30, and from here, let's jump 10 minutes.
03:53Now we are at 3.40.
03:56From 3.40, we only need to jump 3 more minutes.
04:01To finish the problem, we just need to add up the amount of jumps that we did.
04:07We jumped 2 hours, then 15 minutes plus 10 minutes gives us 25 minutes.
04:14And the last jump is 3 minutes added to the 25 gives us 28.
04:20So the answer is 2 hours and 28 minutes.
04:24That is how long it took Katie to eat her lollipop.
04:27Great job, guys!
04:29Let's look at one more using a number line again.
04:35Bill played with his friend for 2 hours and 15 minutes.
04:38If Bill arrived at his friend's house at 3.15 PM, when did he leave?
04:43The problem tells us that Bill got to his friend's house at 3.15 PM and stayed there for 2 hours and 15 minutes.
04:52So we need to use the number line to add 2 hours and 15 minutes to see when he left.
04:57Here is the start at 3.15 PM.
05:00We start by jumping with the highest increment we can, which is the hour.
05:04Let's jump 2 hours.
05:07We have jumped 2 hours and we are at 5.15 PM.
05:15Great job!
05:16Now all that's left is to jump another 15 minutes.
05:19So what time did Bill leave his friend's house?
05:245.30 PM.
05:25Great job!
05:26He left at 5.30 PM.
05:27Thank you for learning with me today.
05:28I got a jet.
05:29See you guys later!
05:30See you guys later!
05:36See you guys later!
05:37See you guys later!
