Can you solve the bridge riddle? - Alex Gendler

22,550,284 views ใƒป 2015-09-01

TED-Ed


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: Tal Dekkers
00:09
Taking that internship in a remote mountain lab
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ืœืงื™ื—ืช ื”ื”ืชืžื—ื•ืช ื”ื”ื™ื ื‘ืžืขื‘ื“ืช ื”ืจ ืžืจื•ื—ืงืช
00:12
might not have been the best idea.
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ืื•ืœื™ ืœื ื”ื™ืชื” ื”ืจืขื™ื•ืŸ ื”ื›ื™ ื˜ื•ื‘.
00:14
Pulling that lever with the skull symbol just to see what it did
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ืžืฉื™ื›ืช ื”ื™ื“ื™ืช ืขื ืกืžืœ ื”ื’ื•ืœื’ื•ืœืช ืจืง ื›ื“ื™ ืœืจืื•ืช ืžื” ื”ื™ื ืขื•ืฉื”
00:18
probably wasn't so smart, either,
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ื›ื ืจืื” ื’ื ืœื ื”ื™ืชื” ื”ื›ื™ ื—ื›ืžื”,
00:20
but now is not the time for regrets
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ืื‘ืœ ืขื›ืฉื™ื• ืœื ื”ื–ืžืŸ ืœื—ืจื˜ื•ืช
00:23
because you need to get away from these mutant zombies fast.
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ืžืคื ื™ ืฉืืชื ืฆืจื™ื›ื™ื ืœื‘ืจื•ื— ืžื”ื–ื•ืžื‘ื™ื ื”ืžื•ื˜ื ื˜ื™ื ื”ืืœื” ืžื”ืจ.
00:28
With you are the janitor, the lab assistant, and the old professor.
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ืื™ืชื›ื ื ืžืฆื ื”ืฉืจืช, ืขื•ื–ืจืช ื”ืžืขื‘ื“ื”, ื•ื”ืคืจื•ืคืกื•ืจ ื”ื–ืงืŸ.
00:32
You've gotten a headstart, but there's only one way to safety:
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ื™ืฉ ืœื›ื ื™ืชืจื•ืŸ ื”ืชื—ืœืชื™, ืื‘ืœ ื™ืฉ ืจืง ื“ืจืš ืื—ืช ืœื‘ื™ื˜ื—ื•ืŸ:
00:36
across an old rope bridge spanning a massive gorge.
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ืžืขืœ ื’ืฉืจ ื—ื‘ืœื™ื ื™ืฉืŸ ืฉืžืชื•ื— ืžืขืœ ืชื”ื•ื ืขืฆื•ืžื”.
00:40
You can dash across in a minute,
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ืืชื ื™ื›ื•ืœื™ื ืœืจื•ืฅ ืœืจื•ื—ื‘ื• ื‘ื“ืงื”,
00:42
while the lab assistant takes two minutes.
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ื‘ืขื•ื“ ืœืขื•ื–ืจืช ื”ืžืขื‘ื“ื” ื™ืงื— ืฉืชื™ ื“ืงื•ืช.
00:46
The janitor is a bit slower and needs five minutes,
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ื”ืฉืจืช ืžืขื˜ ืื™ื˜ื™ ื™ื•ืชืจ ื•ืฆืจื™ืš ื—ืžืฉ ื“ืงื•ืช,
00:49
and the professor takes a whole ten minutes,
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ื•ื”ืคืจื•ืคืกื•ืจ ืฆืจื™ืš ืขืฉืจ ื“ืงื•ืช ืฉืœืžื•ืช,
00:52
holding onto the ropes every step of the way.
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ื›ืฉื”ื•ื ืžื—ื–ื™ืง ื‘ื—ื‘ืœื™ื ื›ืœ ืฆืขื“ ื•ืฆืขื“.
00:56
By the professor's calculations,
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ืœืคื™ ื—ื™ืฉื•ื‘ื™ ื”ืคืจื•ืคืกื•ืจ,
00:58
the zombies will catch up to you in just over 17 minutes,
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ื”ื–ื•ืžื‘ื™ื ื™ื“ื‘ื™ืงื• ืืชื›ื ืชื•ืš 17 ื“ืงื•ืช ื‘ืœื‘ื“,
01:02
so you only have that much time to get everyone across and cut the ropes.
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ืื– ื™ืฉ ืœื›ื ืจืง ืืช ื”ื–ืžืŸ ื”ื–ื” ื›ื“ื™ ืœื”ืขื‘ื™ืจ ืืช ื›ื•ืœื ื•ืœื—ืชื•ืš ืืช ื”ื—ื‘ืœื™ื.
01:08
Unfortunately, the bridge can only hold two people at a time.
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ืœืžืจื‘ื” ื”ืฆืขืจ, ื”ื’ืฉืจ ื™ื›ื•ืœ ืœื”ื—ื–ื™ืง ืจืง ืฉื ื™ ืื ืฉื™ื ื‘ื›ืœ ืจื’ืข.
01:13
To make matters worse,
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ื›ื“ื™ ืœื”ื—ืžื™ืจ ืืช ื”ืขื ื™ื™ื ื™ื,
01:14
it's so dark out that you can barely see,
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ื–ื” ื›ืœ ื›ืš ื—ืฉื•ืš ืฉืืชื ื‘ืงื•ืฉื™ ื™ื›ื•ืœื™ื ืœืจืื•ืช,
01:16
and the old lantern you grabbed on your way only illuminates a tiny area.
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ื•ื”ืขืฉืฉื™ืช ื”ืขืชื™ืงื” ืฉืžืฆืืชื ื‘ื“ืจืš ืžืื™ืจื” ืจืง ืื–ื•ืจ ืงื˜ืŸ.
01:21
Can you figure out a way to have everyone escape in time?
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ื”ืื ืืชื ื™ื›ื•ืœื™ื ืœื—ืฉื•ื‘ ืขืœ ื“ืจืš ื‘ื” ื›ื•ืœื ื™ื‘ืจื—ื• ื‘ื–ืžืŸ?
01:26
Remember: no more than two people can cross the bridge together,
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ื–ื›ืจื•: ืืกื•ืจ ืœื™ื•ืชืจ ืžืฉื ื™ ืื ืฉื™ื ืœื”ื™ื•ืช ืขืœ ื”ื’ืฉืจ ื‘ืื•ืชื• ื–ืžืŸ,
01:30
anyone crossing must either hold the lantern or stay right next to it,
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ื›ืœ ืžื™ ืฉืขื•ื‘ืจ ืฆืจื™ืš ืœืฉืืช ืืช ื”ืขืฉืฉื™ืช ืื• ืœื”ื™ื•ืช ืœื™ื“ื”,
01:35
and any of you can safely wait in the dark on either side of the gorge.
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ื•ื›ืœ ืื—ื“ ืžื›ื ื™ื›ื•ืœ ืœื—ื›ื•ืช ื‘ื—ืฉื›ื” ื‘ื›ืœ ืฆื“ ืฉืœ ื”ืชื”ื•ื.
01:40
Most importantly, everyone must be safely across before the zombies arrive.
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ื•ื”ื›ื™ ื—ืฉื•ื‘, ื›ื•ืœื ืฆืจื™ื›ื™ื ืœืขื‘ื•ืจ ื‘ื‘ื˜ื—ื” ืœืคื ื™ ืฉื”ื–ื•ืžื‘ื™ื ื™ื’ื™ืขื•.
01:45
Otherwise, the first zombie could step on the bridge while people are still on it.
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ืื—ืจืช, ื”ื–ื•ืžื‘ื™ ื”ืจืืฉื•ืŸ ื™ื•ื›ืœ ืœืขืœื•ืช ืขืœ ื”ื’ืฉืจ ื›ืฉืื ืฉื™ื ืขื“ื™ื™ืŸ ืขืœื™ื•.
01:50
Finally, there are no tricks to use here.
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ืœื‘ืกื•ืฃ, ืื™ืŸ ื˜ืจื™ืงื™ื ืœื”ืฉืชืžืฉ ื‘ื”ื ืคื”.
01:53
You can't swing across,
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ืืชื ืœื ื™ื›ื•ืœื™ื ืœื”ืชื ื“ื ื“ ืœืฆื“ ื”ืฉื ื™,
01:54
use the bridge as a raft,
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ืœื”ืฉืชืžืฉ ื‘ื’ืฉืจ ื›ืจืคืกื•ื“ื”,
01:56
or befriend the zombies.
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ืื• ืœื”ืชื—ื‘ืจ ืขื ื”ื–ื•ืžื‘ื™ื.
01:58
Pause the video now if you want to figure it out for yourself!
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ืขืฆืจื• ืืช ื”ืกืจื˜ื•ืŸ ืขื›ืฉื™ื• ืื ืืชื ืจื•ืฆื™ื ืœืคืชื•ืจ ืืช ื–ื” ื‘ืขืฆืžื›ื!
02:01
Answer in: 3
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ืชืฉื•ื‘ื” ื‘ืขื•ื“: 3
02:03
Answer in: 2
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ืชืฉื•ื‘ื” ื‘ืขื•ื“:2
02:04
Answer in: 1
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ืชืฉื•ื‘ื” ื‘ืขื•ื“:1
02:05
At first it might seem like no matter what you do,
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ื‘ื”ืชื—ืœื” ื ืจืื” ื›ืื™ืœื• ืœื ืžืฉื ื” ืžื” ืชืขืฉื•,
02:08
you're just a minute or two short of time, but there is a way.
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ืชืžื™ื“ ื—ืกืจื•ืช ืœื›ื ื“ืงื” ืื• ืฉืชื™ื™ื, ืื‘ืœ ื™ืฉ ื“ืจืš.
02:12
The key is to minimize the time wasted by the two slowest people
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ื”ืžืคืชื— ื”ื•ื ืœืฆืžืฆื ืืช ื”ื–ืžืŸ ืฉืžื‘ื•ื–ื‘ื– ืขืœ ื™ื“ื™ ืฉื ื™ ื”ืื ืฉื™ื ื”ืื™ื˜ื™ื™ื ื™ื•ืชืจ
02:16
by having them cross together.
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ื‘ื›ืš ืฉื”ื ื™ื—ืฆื• ื™ื—ื“.
02:19
And because you'll need to make a couple of return trips with the lantern,
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ื•ื‘ื’ืœืœ ืฉืฆืจื™ืš ืœืขืฉื•ืช ื›ืžื” ื—ื–ืจื•ืช ืขื ื”ืขืฉืฉื™ืช,
02:22
you'll want to have the fastest people available to do so.
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ืืชื ืชืจืฆื• ืืช ื”ืื ืฉื™ื ื”ืžื”ื™ืจื™ื ื‘ื™ื•ืชืจ ืฉื™ืขืฉื• ื–ืืช.
02:26
So, you and the lab assistant quickly run across with the lantern,
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ืื–, ืืชื ื•ืขื•ื–ืจืช ื”ืžืขื‘ื“ื” ืจืฆื™ื ื‘ืžื”ื™ืจื•ืช ืขื ื”ืขืฉืฉื™ืช,
02:31
though you have to slow down a bit to match her pace.
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ืœืžืจื•ืช ืฉืืชื ืฆืจื™ื›ื™ื ืœื”ืื˜ ืžืขื˜ ื›ื“ื™ ืœื”ืชืื™ื ืœืงืฆื‘ ืฉืœื”.
02:34
After two minutes, both of you are across,
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ืื—ืจื™ ืฉืชื™ ื“ืงื•ืช ืฉื ื™ื›ื ืขื‘ืจืชื,
02:37
and you, as the quickest, run back with the lantern.
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ื•ืืชื, ื›ื”ื›ื™ ืžื”ื™ืจื™ื, ืจืฆื™ื ื—ื–ืจื” ืขื ื”ืขืฉืฉื™ืช.
02:41
Only three minutes have passed.
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ืจืง ืฉืœื•ืฉ ื“ืงื•ืช ืขื‘ืจื•.
02:43
So far, so good.
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ื‘ื™ื ืชื™ื™ื ื”ื›ืœ ื˜ื•ื‘.
02:44
Now comes the hard part.
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ืขื›ืฉื™ื• ืžื’ื™ืข ื”ื—ืœืง ื”ืงืฉื”.
02:46
The professor and the janitor take the lantern and cross together.
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ื”ืคืจื•ืคืกื•ืจ ื•ื”ืฉืจืช ืœื•ืงื—ื™ื ืืช ื”ืขืฉืฉื™ืช ื•ืขื•ื‘ืจื™ื ื™ื—ื“.
02:50
This takes them ten minutes
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ื–ื” ืœื•ืงื— ืขืฉืจ ื“ืงื•ืช
02:51
since the janitor has to slow down for the old professor
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ืžืื—ืจ ื•ื”ืฉืจืช ืฆืจื™ืš ืœื”ืื˜ ืขื‘ื•ืจ ื”ืคืจื•ืคืกื•ืจ ื”ื–ืงืŸ
02:55
who keeps muttering
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ืฉืžืžืฉื™ืš ืœืžืœืžืœ
02:56
that he probably shouldn't have given the zombies night vision.
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ืฉื”ื•ื ื›ื ืจืื” ืœื ื”ื™ื” ืฆืจื™ืš ืœืชืช ืœื–ื•ืžื‘ื™ื ืจืื™ื™ืช ืœื™ืœื”.
02:59
By the time they're across, there are only four minutes left,
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ืขื“ ืฉื”ื ืขื•ื‘ืจื™ื, ื™ืฉ ืจืง ืขื•ื“ ืืจื‘ืข ื“ืงื•ืช,
03:03
and you're still stuck on the wrong side of the bridge.
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ื•ืืชื ืขื“ื™ื™ืŸ ืชืงื•ืขื™ื ื‘ืฆื“ ื”ืœื ื ื›ื•ืŸ ืฉืœ ื”ื’ืฉืจ.
03:05
But remember, the lab assistant has been waiting on the other side,
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ืื‘ืœ ื–ื›ืจื•, ืขื•ื–ืจืช ื”ืžืขื‘ื“ื” ื—ื™ื›ืชื” ื‘ืฆื“ ื”ืฉื ื™,
03:10
and she's the second fastest of the group.
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ื•ื”ื™ื ื”ืฉื ื™ื” ื”ื›ื™ ืžื”ื™ืจื” ื‘ืงื‘ื•ืฆื”.
03:13
So she grabs the lantern from the professor
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ืื– ื”ื™ื ืœื•ืงื—ืช ืืช ื”ืขืฉืฉื™ืช ืžื”ืคืจื•ืคืกื•ืจ
03:16
and runs back across to you.
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ื•ืจืฆื” ื—ื–ืจื” ืืœื™ื›ื.
03:18
Now with only two minutes left, the two of you make the final crossing.
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ืขื›ืฉื™ื• ืขื ืจืง ืฉืชื™ ื“ืงื•ืช ืฉื ื•ืชืจื•, ืฉื ื™ื›ื ืขื•ืฉื™ื ืืช ื”ื—ืฆื™ื” ื”ืื—ืจื•ื ื”.
03:23
As you step on the far side of the gorge,
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ื›ืฉืืชื ื“ื•ืจื›ื™ื ืขืœ ื”ืงืฆื” ื”ืฉื ื™ ืฉืœ ื”ืชื”ื•ื,
03:25
you cut the ropes and collapse the bridge behind you,
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ืืชื ื—ื•ืชื›ื™ื ืืช ื”ื—ื‘ืœื™ื ื•ืžืžื•ื˜ื˜ื™ื ืืช ื”ื’ืฉืจ ืžืื—ื•ืจื™ื›ื,
03:28
just in the nick of time.
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ืžืžืฉ ื‘ืจื’ืข ื”ืื—ืจื•ืŸ.
03:30
Maybe next summer, you'll just stick to the library.
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ืื•ืœื™ ื‘ืงื™ืฅ ื”ื‘ื, ืืชื ืชื™ืฉืืจื• ื‘ืกืคืจื™ื”.
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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