Finding the end time for a movie in 24 hour time | Math | Khan Academy


– [Instructor] We are told
that Andre goes to a movie that starts at 19 hours 45 minutes, or 19:45, and is 90 minutes long. What time is the movie finished? So pause this video, and
see if you can answer that before we work through it together. All right, so what I like to do is set up what we could call a timeline. So if this is our timeline, and let’s say that this is
19 hours right over here, 19 hours, maybe this is 20 hours right over there, and then this would be 21
hours right over there. Now, what time does the movie start? It starts at 19 hours 45 minutes. So this would be 19 hours 30 minutes, which would be halfway
between 19 hours and 20 hours, and 19 hours 45 minutes would be halfway between 19:30 and 20. So 19 hours and 45 would
be right over there. So let me write that down. That is 19 hours and 45 minutes, and that is when this
movie is going to start. Now, it’s going to
continue for 90 minutes. So when does it end? So there’s a couple of ways
you could think about it. The way I think about it is
it will take us 15 minutes to get to 20 hours, so that’s 15 minutes. And so 15 minutes of the movie
has happened by 20 hours. And then how much is left? Well, 19 minus 15 is 75, so then there’s another 75 minutes left. Well, 60 of those 75 are gonna
get you to the next hour, so then it’s going to be like this. So then you’re going to
have another 60 minutes to get to the next hour. So, so far we’ve used 75, and then you’re going to
need another 15 minutes to have a total of 90 minutes. So then you’re going to
have another 15 minutes. And so when does the movie end? Well, as you can see, we started at 19:45, 15 minutes got us to 20, another 60 minutes got us to 21, so now we have a total of 75. And then another 15 would
give us a total of 90, so we are finishing 15 minutes after the 21st hour or after hour 21 or however
you wanna think about it. So this time right over here is going to be 21 hours and 15 minutes, or 21:15. So that’s the time that
the movie is finished.

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