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- [Instructor] Hello.
So we're told Colette rides her bike home
from school every afternoon.
She leaves school at 14:55 and arrives home at 15:25.
How long does she ride her bike?
So pause this video, like always,
and see if you can answer that question.
How long is her bike ride home?
All right,
now to help us answer that question,
I'm going to set up a timeline.
So that's my timeline there,
and let's say that, let's see.
Everything is going on between 14 hours
and it looks like between actually past 15 hours
so I'll go to 16 hours,
so that is 14 hours
and this is 15 hours
and then 16 hours would be maybe right over here, 16 hours,
and this would be 14 and a half,
just to make things a little bit clearer.
This would be 15 and a half, just like that.
Actually, it'd be a little bit,
it would be something like that,
and so let's see.
She leaves school at 14:55.
Where is that on this timeline?
Well, 14:55 is five minutes before 15,
so it's going to be roughly right over here.
So that is when Colette leaves,
so that is 14:55,
and then when she arrives, 15:25,
that's 25 minutes after 15 hours,
so that is right over there,
so this right over there is when she arrives home, 15:25,
and so how long is that?
Well the way I think about it is
if we go from 14:55 to 15,
that is five minutes,
so this part right over there is five,
and then to go from 15 to 15:25,
that's another 25 minutes.
So the total,
the total length of her trip in time
is going to be five minutes plus 25 minutes.
Five plus 25 is 30, 30 minutes,
and we are done.


Length of a trip in 24 hour time | Math | Khan Academy

林宜悉 2020 年 3 月 31 日 に公開
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